Observe application activation as well as focus changes.
Observe application activation as well as focus changes.

Fixes #19

The problem is that focus notifications only happen for intra-application window
focuses, but activation notifications will catch inter-application window
focuses.

egabancho/Amethyst,olsonpm/Amethyst,olsonpm/Amethyst,cevaris/Amethyst,ianyh/Amethyst,ianyh/Amethyst,egabancho/Amethyst,ianyh/Amethyst,m4rw3r/Amethyst,ianyh/Amethyst,hooplaaa/Amethyst,hooplaaa/Amethyst,ianyh/Amethyst,m4rw3r/Amethyst,cevaris/Amethyst