Tftd compatibility - underwater concept

Introduction of underwater concept:
Ruleset:
- items(including Vehicles) have 2 properties: useSurface (default true) and useSubmerged (default false)
- crafts/ufos have 3 properties: amphibious (default false) - may submerge, engageSurface(default true) - may engage UFO's surfaced, engageSubmerged(default false) - may engage UFO's submerged
- craft weapons have 2 properties: useSurface (default true) and useSubmerged (default false), and a new movement type - float ("fly" underwater only)
- armors have one proprety: amphibious (default false)
- alien races have 2 properties: useSurface (default true) and useSubmerged (default false) i.e. may appear on surface and/or underwater
- added negative heights (i.e. depths) to trajectories



Mechanics:
- UFO's - savegame no more compatible, ufo height/depth is the corresponding number, added new states - navigating and touched down
- an UFO pursuit can end in dogfight only if engageSurface/engageSubmerge/amphibious conditions met, 
- cannot engage popup created as a variant of craft status...
- dogfight considers only applicable weapons when cautious or standard attack is made depending on craft weapons usage and height/depth
- an amphibious UFO shot down on water generates mission, a non-amphibious doesn't (is destroyed)
- the battlescape generator memorizes underwater mission, in order to properly deploy aliens - imagined a separate set of deployments (same as land and "_SUBMERGED" appended in order to fully separate them)
- battle units (player) incompatible with mission type (pure surface while underwater or opposed) are idle (frozen tu's=0)
- items incompatible with mission may not be used (i.e. same error style as empty weapon clip)
- created strings