Also:
- Add use_tensorial_basis parameter allowing run-time choice of basis.
- Remove degree argument from solveTof() method, degree is instead obtained
from parameters in constructors. Modified compute_tof* programs to match.
The limiter is experimental and unfinished, untested work in progress.
Limiter is therefore inactive by default.
Also fixed a minor bug: use_cvi_ was not initialized.
The class TransportModelTracerTofDiscGal now uses
VelocityInterpolationInterface, and acts as a factory
internally, choosing an interpolation method depending on
the parameter 'use_cvi'.