Update Gradle plugin.

Compatibility with Android Studio 0.9.1.
Merge pull request #16 from learning-layers/hotfix/update-gradle-plugin

Update Gradle plugin.
Add Retrofit dependency.
Implement osTicket integration.

Users can now send feedback from within the app.
Display an error dialog if feedback can’t be sent.
Replace placeholder text.
Capitalise 'OK' in strings.
FeedbackDialogFragment implements the callback.
Use constants.
Clarifying comments, cleanup.
Clean up feedback dialog layout a bit.
Retain context in FeedbackDialogFragment.
Added AppCompat v7:21 to support new stuff in 5.0
Merge branch 'integration' into improvement/LL-831

Conflicts:
	build.gradle
	gradle/wrapper/gradle-wrapper.properties
Merge pull request #22 from learning-layers/feature/LL-821

Add feedback system.
Merge branch 'integration' into improvement/LL-831

Conflicts:
	build.gradle
	gradle/wrapper/gradle-wrapper.properties
Just in case
Safety commit