Users can now add and remove squadrons with specific buttons. this also allows new aircraft types to be added as well.
- rebased existing PR to develop
- reverted observable and changed to signals
- changed the general concept so that changes only affect the ui data model and not the game directly. Game will only be updated on apply
- removed unused code
- adopt to review comments
- allow user to choose a predefined squadron preset (also alow none value to use the random generator)
- Reuse the squadron defs from the default assigner in the AirWing class
- allow user to re-roll the squadron nickname (also added new ui icons for the button)
This also does improve the over-purchase problems, though I can't spot
the behavior change that's causing that. Presumably the old
implementation had a bug I can't spot and in rewriting it I solved the
problem...
Fixes https://github.com/dcs-liberation/dcs_liberation/issues/1582
