Add AI Vehicles Equivalent To All Drivable Tanks

[MajorMagee]

Type of improvement: AI

Explanation of proposals: Add simplified AI vehicle equivalents for all of the player drivable ones in Tank Crew. For example the SU 122 and SU 152 only exist as _su122, and _su152 versions when selecting vehicles in the mission editor. Other candidates for addition to the AI list would be _churchill-iv, _gaz-mm, _pzv-d, _sdkfz10, _sdkfz184

Benefits: The AI versions of vehicles are treated differently in the game than the fully modeled ones. One particular example is that the detailed models disappear from the game 24 seconds after they are destroyed, but the AI versions stay around for 5 minutes. The mission builder can designate either type to last forever, but if 5 minutes is sufficient for believable results (24 seconds is not) you don't have any option to do that for the detailed models.