Blender Git Loki

GPencil: Set active layer when click in Dopesheet keyframe area

Now, when clicking in the keys area, the layer is synchronized, not only in the left area with the names. This is one of the most requested feature by artists.

Also, removed some old comments.

Reviewers: brecht, angavrilov

Reviewed By: brecht

Subscribers: pepeland, mendio

Differential Revision: https://developer.blender.org/D5627