Recorder: Replace icon with something matching

* After the removal of the screen recorder part, the two-sectioned
  icon doesn't really match the app anymore.
* The new icon
  * Uses a microphone icon on the app's accent color
  * Adds a little shadow to not appear flat
  * Matches the design language of other app icons, e.g. the dialer

Change-Id: I3623b9d2b3c559ba50260aeddb08a06cd4e61eba