Basic UI components

- Add first preliminary model of building and working with
  higher level components.
- Components for text input, path input, single selector and
  multi selector.
- Components renderings are based on ANTLR ST templates while
  there is support for building rendering output manually.
- Add these into sample.
- This is a base of additional work what goes to these components
  and concepts around it.
- Relates #360

spring-shell-core/src/main/resources/org/springframework/shell/component/multi-item-selector-default.stg

@@ -0,0 +1,64 @@
+// used to select style if item is selected/unselected
+selected_style(flag) ::= <%
+<if(flag)>item-selected<else>item-unselected<endif>
+%>
+
+// selector rows
+select_item(item) ::= <%
+<if(item.onrow)>
+  <("> "); format="item-selector">
+<else>
+  <("  ")>
+<endif>
+
+<if(item.enabled)>
+  <if(item.selected)>
+    <("[x]"); format=selected_style(item.selected)> <item.name>
+  <else>
+    <("[ ]"); format=selected_style(item.selected)> <item.name>
+  <endif>
+<else>
+  <("[ ]"); format="item-disabled"> <item.name; format="item-disabled">
+<endif>
+%>
+
+// start '? xxx' shows both running and result
+question_name(model) ::= <<
+<("?"); format="list-value"> <model.name; format="title">
+>>
+
+// within info section, dedicated instructions for user
+info_filter(model) ::= <%
+<if(model.input)>
+, filtering '<model.input>'
+<else>
+, type to filter
+<endif>
+%>
+
+// info section after '? xxx'
+info(model) ::= <<
+[Use arrows to move]<info_filter(model)>
+>>
+
+// get comma delited string
+comma_delimited(values) ::= <%
+<values; separator=",">
+%>
+
+// component result
+result(model) ::= <<
+<question_name(model)> <(comma_delimited(model.values)); format="value">
+>>
+
+// component is running
+running(model) ::= <<
+<question_name(model)> <info(model)>
+<model.rows:{x|<select_item(x)>}; separator="\n">
+>>
+
+// main - hardcoded name
+// model - model built by MultiItemSelectorContext
+main(model) ::= <<
+<if(model.isResult)><result(model)><else><running(model)><endif>
+>>

spring-shell-core/src/main/resources/org/springframework/shell/component/path-input-default.stg

@@ -0,0 +1,38 @@
+// message
+message(model) ::= <%
+<if(model.message && model.hasMessageLevelError)>
+<(">>>"); format="level-error"> <model.message; format="level-error">
+<elseif(model.message && model.hasMessageLevelWarn)>
+<(">>"); format="level-warn"> <model.message; format="level-warn">
+<elseif(model.message && model.hasMessageLevelInfo)>
+<(">"); format="level-info"> <model.message; format="level-info">
+<endif>
+%>
+
+// info section after '? xxx'
+info(model) ::= <%
+<if(model.input)>
+<model.input>
+<endif>
+%>
+
+// start '? xxx' shows both running and result
+question_name(model) ::= <<
+<("?"); format="list-value"> <model.name; format="title">
+>>
+
+// component result
+result(model) ::= <<
+<question_name(model)> <model.resultValue; format="value">
+>>
+
+// component is running
+running(model) ::= <<
+<question_name(model)> <info(model)>
+<message(model)>
+>>
+
+// main
+main(model) ::= <<
+<if(model.resultValue)><result(model)><else><running(model)><endif>
+>>

spring-shell-core/src/main/resources/org/springframework/shell/component/single-item-selector-default.stg

@@ -0,0 +1,44 @@
+// selector rows
+select_item(item) ::= <%
+<if(item.selected)>
+<("> "); format="item-selector"><item.name; format="item-selector">
+<else>
+<("  ")><item.name>
+<endif>
+%>
+
+// start '? xxx' shows both running and result
+question_name(model) ::= <<
+<("?"); format="list-value"> <model.name; format="title">
+>>
+
+// within info section, dedicated instructions for user
+info_filter(model) ::= <%
+<if(model.input)>
+, filtering '<model.input>'
+<else>
+, type to filter
+<endif>
+%>
+
+// info section after '? xxx'
+info(model) ::= <<
+[Use arrows to move]<info_filter(model)>
+>>
+
+// component result
+result(model) ::= <<
+<question_name(model)> <model.value; format="value">
+>>
+
+// component is running
+running(model) ::= <<
+<question_name(model)> <info(model)>
+<model.rows:{x|<select_item(x)>}; separator="\n">
+>>
+
+// main - hardcoded name
+// model - model built by SingleItemSelectorContext
+main(model) ::= <<
+<if(model.isResult)><result(model)><else><running(model)><endif>
+>>

spring-shell-core/src/main/resources/org/springframework/shell/component/string-input-default.stg

@@ -0,0 +1,28 @@
+// info section after '? xxx'
+info(model) ::= <%
+<if(model.input)>
+<model.input>
+<else>
+<("[Default "); format="value"><model.defaultValue; format="value"><("]"); format="value">
+<endif>
+%>
+
+// start '? xxx' shows both running and result
+question_name(model) ::= <<
+<("?"); format="list-value"> <model.name; format="title">
+>>
+
+// component result
+result(model) ::= <<
+<question_name(model)> <model.resultValue; format="value">
+>>
+
+// component is running
+running(model) ::= <<
+<question_name(model)> <info(model)>
+>>
+
+// main
+main(model) ::= <<
+<if(model.resultValue)><result(model)><else><running(model)><endif>
+>>