Align popup footer buttons to take 50% width each
The alignment of the buttons was done haphazadly before, using
padding. This should be done better; we should calculate the buttons
width to be 50% of the width of the popup.
Since the popup accepts a width config, we know what its value is,
and can calculate the proper width. The width was added to the
variables.less file for continued use.
- Added popupWidth config variable to the badge widget
- Added OO.ui.ButtonGroupWidget to place the buttons in for consistency and styling
- Added calculated width styles to both footer buttons
- Added corrections for MonoBook
(cherry picked from commit a37e764d3d169a583410e027d8a035884338626d)