Move to Gradle-based build system

* NineOldAndroid is now referenced through Maven
  (not a submodule anymore)
* The module names have been changed
* Lotsa refactorings (using an activity-alias for the
  sample Activity to avoid messing stuff with the new
  package name for it)
* Removed all the old stuff, including IDEA and Eclipse
  projects (they didn’t work very well anyway)
* Added TargetApi annotations wherever possible
* Tested on Genymotion Nexus One (2.3.7) image