Support xxhdpi launcher icon

[johnteslade]

The launcher icon for this app on my Nexus 5 does not look as sharp as the other icons on my home screen. The screen on this phone has 445dpi ("xxhdpi" Android setting) and looking at the source code there is no resources for this screen density.

According to http://developer.android.com/design/style/iconography.html the xxhdpi launcher icon should be 144x144 pixels in size.

BTW - love the app, use it every day.