General project/build update

- Updates all Gradle dependencies to the latest version, making this project compatible with Android Studio 0.8.4
- The app now targets the latest sdk 20.
- Also updates the .gitignore and fixes a dependency issue (showcaseview 5.0.0-SNAPSHOT was not available, changed it to 5.0.0).
- Replaced .gitignore with a standard Android gitignore.