Fix for an unexpected interaction between the GTS rework and Choose My Class

Guerilla Tactics School - Death And Taxes
- Starts with only a small selection of classes available.
- To unlock additional classes in the GTS, a soldier of that class must be leveled to Level 6, and then unlocked in the GTS unlocks.

Further covert operations tweaks and adjustments.
Plasma Edged sword very slightly, and I mean very slightly, buffed.

Changed a questionable Long War change that made Gatekeeper Beam attacks invalidated by Fortress, as well as many other perks, and buffed the beam attack slightly.

Chemthrowers rebalanced.

- Immolator Burn now uses a special aim Roll that prefers flanks.
- Immolator Damage Adjusted.
- Cryolator Damage Adjusted.
- Immolators and Cryolators
- Instead of dealing no damage, these chemthowers now instead deal half damage to targets that would be immune to their respective status effect.

Some nerfs for some egregiously overpowered weapons.

Gunnery Sergeants and Master Sergeants are effectively banned from the Black Market. Because reasons.

Some enhancements to improve player experience

Standard Melee Tree Progression no longer requires corpses.
Campaign start is slightly more forgiving.
Adjusted some outlier weaponry.
Avatar project begins slightly later.
Overall campaign difficulty remains very extreme.

Updates and stuff