Convert to gradle and bundle number-picker

The reason why I am still using your time-picker in my gradle projects is because you have custom dialogs with extra functionality over android's regular timepicker and numberpicker.

This will allow others to use android-timepicker in gradle projects, and skip adding number-picker as a dependency.

Just add `android-timepicker` in your **settings.gradle**:

```gradle
include ':Libraries:android-timepicker'
```

Also add the dependency to your project's **build.gradle**:

```gradle
compile project(':Libraries:android-timepicker')
```

Moveover, this pull request will allow you to add android-timepicker to maven as a gradle project.