Fix alias usage with Command annotation

- Fix alias command extraction from existing @Command
  annotations so that we actually get multiple aliases
  defined if more than one defined on a method level.
- Fix rendering issue in a help stg template when
  multiple aliases exists.
- Fixes #796

spring-shell-standard-commands/src/main/resources/template/help-command-default.stg

@@ -70,7 +70,7 @@ availability(availability) ::= <<
 aliases(aliases) ::= <<
 <if(aliases)>
 <("ALSO KNOWN AS"); format="style-highlight">
-       <(aliases); separator=", ">
+       <aliases: { a | <a>}; separator=", ">
 <endif>
 >>