Maven support for library and example app

This pull request is an example of Maven support for SlidingMenu which can serve as a starting point for a discussion on Maven support. There are several challenges supporting Maven for SlidingMenu:

* You will need to release/tag stable versions of the library. Preferrably in Sonatype OSS repository (https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide) in order for people to easily start using the library.

* The maps dependency in the library is not available from any public repository. Building and using the library will require users to deploy the maps artifact to their own private Maven repository. This can be done using https://github.com/mosabua/maven-android-sdk-deployer.

* Because library projects are included and rebuilt inside the projects that include them all projects using the SlidingMenu library will have a dependency to Maps API and ActionBarSherlock. This isn't really good because people will have to include it with their apps even though they're not using those libraries. This may be possible to work around by moving the library code that is dependent on Maps API and ActionBarSherlock into separate modules. Users would only depend on the core library if they don't need ActionBarSherlock or Maps. A proposed project structure:

slidingmenu-parent
|->slidingmenu-core
|->slidingmenu-maps-support
|->slidingmenu-abs-support
|->example