Make vehicles slow down on slopes

[MHeasell]

In TA, vehicles (probably any unit that aligns to a slope) move slower horizontally when they are on sloping terrain. Kbots however do not seem to slow down when moving over slope.

In RWE units all move at the same horizontal speed regardless of slope.

Current understanding is that units that align themselves with the slope should move slower when they are on the slope. Units that are always upright have their horizontal speed unaffected by slope. This suggests that speed should be a function of the unit's current slope (upright units always having no slope).