VTOL infantry fixes

[neoancient]

Fixes four issues with VTOL infantry movement:

1. Disables the jump button on the movement panel. The jump button gets enabled because infantry use jump MP for VTOL or underwater movement.
2. getMovementModeAsString() returns VTOL for beast-mounted VTOL infantry rather than trying to assign it a mechanized VTOL movement type.
3. Allows VTOL infantry with 0 ground movement to move horizontally after changing elevation. Spending MP before the first move to a new hex is treating it like 0* MP foot infantry and disallowing further movement after spending MP.
4. Use VTOL or UMU mp instead of ground MP as appropriate when Princess calculates possible paths for infantry.

Fixes #4901.