Rocket: quaternions or matrices optionally with or without Gram-Schmidt

Meant to explore benefits of quaternions vesus matrices and necessity of Gram-Schmidt in the latter case.

To this end common.py contains the following 'switches':

useQuaternions = True
useGramSchmidt = True # Only matters if useQuaternions == False

When using matrices, Gram-Schmidt turns out to be an absolute necessity.
The difference between quaternions and matrices + Gram-Schmidt seems small,
but certain cases were encountered where matrices + Gram-Schmidt became seriously unstable,
whereas quaternions remained stable.
However at the moment unfortunately I cannot reproduce them...

Jacques