Fix memory leaks ; remove useless headers ; use pragma once ; renames of variables herited from gtk3 ; removed unused stuff

[AKArien]

Fixes memory leaks in the various widgets. Mostly happened when reloading the configuration by not disconnecting signals, but in the case of the menu widget, there were also leaks for each show/hide.

For the rest that is on this branch, i’m fully prepared to hear it’s out of the scope of this pr, but oh well, that’s what git cherry-pick is for :

• #pragma once instead of ifdefs
• remove pointless includes
• use <> for includes from libraries and "" for wf-shell headers
• split WayfireMenu::update_popover_layout into it and setup_popover_layout for clarity
• change hbox to box in WayfireStatusNotifier

[AKArien]

Marking as draft, as the tray widget still has a memory leak when reloaded, and i’ve not gotten to test the notifications and command-output changes.

[trigg]

Overall looks very good. Ran and did some testing and see no negatives.

Tray in its current incarnation is an abomination I designed with no previous understanding of dbus, I'm not too surprised it has leaks.

[AKArien]

@trigg made a clean history, and i think that’s all for me.
There is still what i think is a memory leak, as i doubt that’s intended behaviour, but in the notifications widget, i don’t think any memory that is taken when recieving a notification is ever freed. i think it will have to wait for a better soul to fix it, because i can’t say i understand it.
I also did the hbox->box style change in menu and notifications widget.

[trigg]

Sorry about the delay, LGTM.

Tried each and no issues found.