Add option: notification on playback resume (#196)

* Add option: notification on playback resume

This adds an optional setting to show the
notification that is displayed when changing
the track when resuming playback as well.

* Modify resume notification calling

This adds a new signal "Resumed" that is emitted
when the player status is changed from Paused
to Playing.
The AlbumArtLoaded function will only be called
again when playback is manually resumed, and not
when the player is started for the first time
or when the track is changed.

src/core/player.cpp

@@ -450,6 +450,7 @@ void Player::PlayPause() {
   switch (engine_->state()) {
     case Engine::Paused:
       engine_->Unpause();
+      emit Resumed();
       break;
 
     case Engine::Playing: {