Constructors for Euler angles

[eggrobin]

Rotations need a constructor from Euler angles.
The convention should be an enum offering all possibilities (ZXZ, XYX, YZY, ZYZ, XZX, YXY).
While we're at it, a constructor from Cardan-Tait-Bryan (heading-elevation-bank, yaw-pitch-roll) angles should be provided (again with all conventions XYZ YZX ZXY XZY ZYX YXZ, for which we already have a type).
Beware the Jabberwock! game developers, being confused about geometry, call Cardan-Tait-Bryan angles Euler angles.