Polish
Add @SpringBootApplication annotation

Add a new @SpringBootApplication which is equivalent to @Configuration,
@EnableAutoConfiguration and @ComponentScan.

See gh-1842
Document @SpringBootApplication

Add a section to the reference guide about @SpringBootApplication.

See gh-1842
Update samples to use @SpringBootApplication

Update the relevant samples to use the new @SpringBootApplication
annotation.

Closes gh-1842
Merge branch 'gh-1842'