Cook a way to load a Custom Scaler for a **complete** Scale Engine replacement

[Lisias]

As the title says.

Since TS 2.5.0.50 it's theoretically possible for a 3rd Party to completely replace the TweakScale scaling engine with something else. It only happens that TweakScale doesn't have any code to find and load such DLL instead of going for the TS ones.

Define and code a way to allow TweakScale to find a Scale Engine replacement and load it instead of the Default ones.