Blender Git Loki

Fix a bunch of temp full-screen glitches

Steps to reproduce fixed glitches were:
* Change any editor to be file browser from menu, Ctrl+O *from the file browser area*, Esc -> area reset to what it was before changing to file browser initially
* Ctrl+O from any area, F12, Esc -> returns to initial editor in full-screen (expected is file browser in full-screen)

Fixes T46229

Core of the fix is removing old area from spacedata list when going back to previous area (see ED_area_prevspace -> BKE_spacedata_remove). Also, when creating a new temp area we now don't exit old area anymore (needed so SpaceFile->op is kept, but it also makes sense in general)
Aaand finally removes some ugly hacks.

Tested quite a bit, so I think it's safe to apply (besides of remark below), just would like to get things double checked and confirmed. After all, this full-screen stuff finally starts to feel like it's working :P

Note, there's still a memory leak when quitting Blender with temp area open. Haven't found out how to solve yet, but it's not that important for review anyway.

Reviewers: campbellbarton, brecht

Reviewed By: brecht

Subscribers: plyczkowski, Blendify

Maniphest Tasks: T46229

Differential Revision: https://developer.blender.org/D1531