UI improvements:
 - Show "(move pending)" on devices that have been reattached.
 - Add a "remove" button to the toolbar for functionality that would otherwise
   only be in the right-click menu.
Fix deleting master pointers
Fixes regression from 02faf9d303c0a863935325174453ad4f3051864b
Pylint is actually kind of annoying sometimes.
Fix window minimum size for new "remove" button.
Add mention of the "remove" button to the Readme.
Update screenshot to show new UI