(arc) menu-hider

This extension is probably overspecialised for anyone else to find interesting
but enjoy it if you do.

I wanted to configure Unite so that the window controls would always appear in
the top left corner without causing any of the other top bar elements to move,
as this is ugly. As I normally have the arc-menu in that corner, I wanted to
hide arc-menu when a window is maximised to replace it with the window
controls, and if you customise the arc-menu label, it can be exactly the same
size as the window controls so that nothing moves.

This extension handles hiding and showing the arc-menu button as needed. As
for configuring the button to be the right size, I use:

• Apperance: 'Text'
• Show Arrow: False
• Text: ' • • • '