Move project from Maven to Gradle.

* Add Gradle build scripts.
* Change project structure.
* Remove Maven build scripts.
* Remove ProGuard support.
* Remove tests.
Change build instructions for Gradle.
Merge branch 'gradle-migration' into modernization
Change minimum SDK version to 14.

* Remove ActionBarSherlock dependency.
* Change support fragments and activities to framework ones.
Remove ActionBarSherlock mentions.
Fix theme.
Merge branch 'min-sdk-version-14' into modernization
Remove BugSense dependency for license reasons.
Change project package structure and resources.
Refactor list activities and other pieces.
Refactor content provider.
Refactor database classes.
Refactor operations.
Add card and deck models for more easy passing.
Fix database creation issues.
Refactor cards list.
Change models to implement parcelable interface.
Change cards fragments to use models.
Refactor cards pager.
Fix inspection warnings.