OOjs UI: Pull in I959ade244 from v0.5.0 for cherry-pick

Also pull through required items in VisualEditor: Ie335f19 and I2a7df95.

Change-Id: Ib45e321b5218a2e79757a979fae875a3f9127205
Merge "OOjs UI: Pull in I959ade244 from v0.5.0 for cherry-pick" into wmf/1.25wmf12