Add base shell test system

- NOTE: very much wip and unstable
- This commit is a first step to provide boot style
  @ShellTest annotation
- New modules spring-shell-test and spring-shell-test-autoconfigure
- Focus is to autoconfigure context without shell runners so that
  we can create "sessions" and hook to configures jline terminal
  with custom in/out streams.
- Skeleton fork from jediterm to provide basic terminal emulation
  to part of a control amd escape characters working.
- ShellTestClient is a concept user can use to interact with a shell
  in a same way user would use a "real" shell.
- Fixes #489

spring-shell-starters/spring-shell-starter-test/spring-shell-starter-test.gradle

@@ -0,0 +1,12 @@
+plugins {
+	id 'org.springframework.shell.starter'
+}
+
+description = 'Spring Shell Starter Test'
+
+dependencies {
+	management platform(project(":spring-shell-management"))
+	api(project(':spring-shell-starters:spring-shell-starter'))
+	api(project(":spring-shell-test"))
+	api(project(":spring-shell-test-autoconfigure"))
+}