Share button, other header adjustments, and bottom banner ad

Adds share button to article header.  Makes slight adjustments to other header buttons.

There is still a white border around the share-toggle button.  I cannot find it anywhere.  If you have a chance to take a look I'd appreciate it.  Other than that, it seems to be working fine. 

I've added a fixed banner ad along the bottom.  It should work for phones, but might need to be adjusted on tablets.