Rework command subsystem

- Focus of these changes are to introduce a new command system based on
  real registrations (new way) instead of continuously (old way) resolve
  methods and its parameters via reflection.
- There's a lot of changes as this resolution via reflection had its
  hooks almost everywhere and thus most changes are just refactorings.
- Order to understand real changes I'd start to look classes under
  `org.springframework.shell.command` package as it defines new registration,
  catalog and parser classes. Also samples contain new classes to demonstrate
  new functionality.
- Fixes #380

spring-shell-core/pom.xml

@@ -23,6 +23,10 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-validation</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-messaging</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>org.jline</groupId>
 			<artifactId>jline</artifactId>