Triangulate Modifier: using different ngon and quad methods

Quads: Beauty, Fixed, Fixed Alternate, Shortest Diagonal
Ngons: Beauty, Scanfill

* Shortest Diagonal is the default method in the modifier (popular
  elsewhere), but beauty is the default in Ctrl+T).

* Remove the need for output slot and beauty operator to be called
after Clt+T

Patch with collaborations and reviewed by Campbell Barton