Support for notification panel key on ATV

Add activity intents to open and toggle notification panel (requires
STATUS_BAR_SERVICE permission).
Add protected broadcast intent to close notification panel.
Make long-press-on-home configurable to open notification panel.
Create TvNotificationPanel class which forwards notification panel
requests to the configured handler.

Bug: 158661029
Test: manually tested on ATV device with adapted launcher
Change-Id: I555bb3801ac949c8985692b41b02323c56332ccd