Sil's MAD-5A Cannon Fix

For some dumb reason, PGI decided to make the dorsal cannon on the MAD-5A Marauder II only a medium size hardpoint, stopping people from putting an AC/20 or Gauss Rifle there.

I find this decision weird and annoying, so I decided to fix it.  No other changes were made.

The first time you load a save where you own a MAD-5A, you may get an "invalid loadout" notice.  You can continue; the game will have removed something from the 'Mech in order to achieve a valid loadout.

This is the first mod I've ever created, so no promises on it working correctly.  As-is, no warranty, etc.