Add support for beans{} in CLI scripts

User can add (a single) beans{} DSL declaration (see GroovyBeanDefinitionReader
in Spring 4 for more detail) anywhere at the top level of an application source
file. It will be compiled to a closure and fed in to the application context
through a GroovyBeanDefinitionReader. Cool!

The example spring-boot-cli/samples/beans.groovy runs in an integration test
and passes (see SampleIntegrationTests).

spring-boot-cli/samples/beans.groovy

@@ -0,0 +1,13 @@
+@RestController
+class Application {
+	@Autowired
+	String foo
+	@RequestMapping("/")
+	String home() {
+		"Hello ${foo}!"
+	}
+}
+
+beans {
+  foo String, "World"
+}