[WIP] Don't use menubuttons where we don't want buttons

[trigg]

Refactor internal WayfireMenuButton to no longer actually be a menu button

We put a fair bit of extra code to make MenuButton not actually be a menubutton. So this PR will standardise an interface for all Popup-based widgets without each one having to fight to not look like a button

Advantages over not having this PR:

• Fixed popover too big for entire screen at the source
• Moved autohide and layer shell logic out of individual widgets.
• Added option for popup-menu to follow mouse across other popup-menu widgets.

TODOs:

• Reimplement menu fullscreen option
• add some form of css class to signify a widget has a popup shown currently
• add css class to signify it has a popup available to be shown (and unset when not menu and 0 children in popup)