Implement leading color approximation and/or 1/N_C expansion

[ohl]

Leading color ist trivial in O'Mega: just disable the U(1) ghosts and off-diagonal color factors. This is useful beyond the speed-up for matching to parton showers and fragmentation.

Higher orders in the 1/N_C expansion require help from the Fusion functor and could be a good test case for the tagging mechanism. It is not clear that next-to-leading-color is much faster than the full calculation. Therefore it is not clear that implementing the 1/N_C expansion beyond leading order is useful.

[ohl]

Probably not useful.

[Juergen Reuter]

Milestone renamed

[Juergen Reuter]

Milestone renamed