Gradle support

Finally added gradle support for this lib. thanks @wuyingren for you initial commit.
Thanks @wodka for the missing source folder hint in the `build.gradle`

via https://github.com/passsy/android-HoloCircularProgressBar/pull/10

The library is working. The sample is working.


open TODOs before merge:

- [x] simple Eclipse import for the library
- [x] quick start with sample and lib in Eclipse

- [x] simple Android Studio import for the library
- [x] quick start with sample and lib in Android Studio