Improvements to Wikigrok A interface

The main changes are making the interface inline (rather than a
pop-up drawer) and adding a 'more info' overlay.

This is purely an en.wiki experiment for now and will be frequently
changing, so we are not localizing strings yet.

Change-Id: Ifd8d803d8d4437a52af229b19338f9b507be5894
See: https://trello.com/c/7P9KBEwg/1-5-wikigrok-inline-styling
Merge "Improvements to Wikigrok A interface"