Add optional offset and scale attributes to the unit INI

It's not uncommon for unit animations to be slightly offset or off-scale from the baseline standard. Allowing for these to be modified through the INI so that we can account for this without having to edit FLCs.

Example:
```
ANIM_SCALE=95.0
ANIM_OFFSET_X=0
ANIM_OFFSET_Y=-5
```