Advanced Mortars

#1194 
Advanced Mortar (Effected by wind, drag, powder temp) and rangetable.

**WIP** (don't commit)

Not "full-simulation", but It's a much more realistic and challenging system than the A3 mortar.

Model is the just the A3 Mk6 mortar, but has a completely new HUD and interface e.g.: Actually shows current Charge (amount of propellant which effects muzzle velocity)

Simple reskin for the model, not sure if it's worth keeping (about 1 MB).

This is still a WIP, but should be close to feature complete right now.

TODO:
- [ ] - Tweak Config Values (I think powder effect is too high compared to real mortar tables)
- [ ] - Has a "rangefinder" button, figure out how to integrate with AGM_FCS to avoid duplicate button
- [ ] - Localization Hell (lots of little short strings that need to fit into small boxes)
- [ ] - Testing
- [ ] - Add Other Ammo Types?
- [ ] - Possible: add "realistic" loading individual shells and changing fuze settings


Adds:
-Vehicles:
   `B_AGM_advancedMortar`
-Backpacks:
    `B_AGM_Artillery_backpack_tube`
    `B_AGM_Artillery_backpack_baseplate`
-Items:
  `AGM_RangeTable_81mm`