Move mobile ContextItemWidget hacks into separate class

Removes CSS visibility hack and all other traces of mobile from
desktop code.

Change CSS to float 'edit' button right, otherwise it isn't visible
for long link targets. It's not possible to have the text ellipsis
and have text to its right in pure CSS.

Change-Id: I225df7970e113892cc08b44e53f22e32ce4dfee0
Merge "Move mobile ContextItemWidget hacks into separate class"