Gradle build files update to support android-studio v0.6.0

The changes include:
* Update of the `.gitignore` file to ignore the `build` directory generated by android-studio during the build and compilation process.
* Update of the project gradle build file to support `0.6.0` and prior versions of android-studio
* Update of the sub-projects gradle build file in order to upgrade the android build tools to version 19.1.0 (a requirement of android-studio v0.6.0).