Add basic build.gradle for api sub-project.
Add ExtensionData to hold extension details.
Build jar and source jar, add version.
Rename ExtensionData to just Action.
Support Bundle and JSON serialization for Action.
Initial implementation of SeriesGuideExtension.
Fix javadoc.
Subscribers transmit episode info to extension.
Merge branch 'beta' into service-extensions
Add code for built-in trakt extension.
Define extensions intent actions to filter for.
Register trakt extension in manifest.
Simplification.
Started ExtensionManager, can query available extensions.
Make ExtensionManager.getInstance() static.
Add extension query test to overview episode menu.
Merge branch 'beta' into service-extensions
Support enabling and disabling extensions.

- Right now there is no confirmation if subscribing/enabling actually
worked. This will only become apparent if the extension does not deliver
responses, so the user might then try disabling/enabling it again.
Protect against handler modifying subs map while it is iterated over.

- The alternative would be to process subscriptions right after
processing the intent that woke the service up.
Rename subscriptions to subscribers, add min SDK 11 notice.