Consider re-arranging the project structure to mirror Spring Boot

[jxblum]

For example:

1. Move all Starters (e.g. spring-geode-starter*, spring-gemfire-starter* and spring-cloudcache-starter*) to a spring-geode-starters directory.

2. Add all core modules (e.g. spring-geode, spring-geode-autoconfigure, spring-geode-actuator, spring-geode-actuator-autoconfigure, etc) to a spring-geode-project directory.

3. ???

[jxblum]

This task will not be performed/completed until SBDG reaches 2.0.