Resume the Activity from the Cast Notification instead of creating.

Due to our architecture, we can't launch a new activity and jump to the
appropriate place in the app. This allows us to resume where we were,
simply by finding and using the existing Activity, if possible.
Remove the Play / Pause button from Notification.

The user must be in the app to ensure the app is in sync with the remote
media, so they can't resume casting from the notification. They can stop
it completely, or tap the notification to go back to the app and resume
from there.
Remove controls from the lock screen.

As other disabled features, we need the user to control playback from
within the app to ensure sync, so the controls are disabled.
Update the project properties file.

Yeah, it says not to edit it. I'm a rebel like that.
Update project target to Lollipop.