Update and fix build files and project dependencies

This PR
- updates the project to the latest target sdk version
- fixes Maven build problems (android jars for sdk 17+ are not available from Maven Central anymore, so they need to be deployed locally)
- updates the ActionBarSherlock reference from 4.3.1 to 4.4.0
- updates android-maven-plugin reference from 3.6.0 to 3.8.0 (note that Maven 3.1.1+ is required)
- updates a few version numbers that were missed
- adds proper .gitignore files and adds project.properties files which fixes the incorrect sdk level selection after importing

[edit]
I also added the gradle wrapper to source control, since the build was failing due to the Gradle 1.9 update. The Gradle version must be compatible with the Android build tools. The wrapper ensures that the correct version will be used.