Add a gradle wrapper

This should allow painless Android Studio imports.
Merge pull request #55 from hav3n/branch-gradle-wrapper

Add a gradle wrapper
Update gradle wrapper & .gitignore

- Add compatibility for Gradle Version 0.9+
- Ignore Android Studio specific files
Merge pull request #60 from hav3n/branch-gradle-wrapper

Update gradle wrapper & .gitignore
Merge Commit