Move You's n_phi from constraints object to ubcalc.reference - #24

Inorder that n_phi may be calculated from n_hkl and UB, and in the
future from tau and sigma.
ubcalc.reference now can be configured with n_phi or n_hkl - #24

We still need:
1. commands to set n_phi or n_hkl
2. support for, and commands to support sigma and tau (and to display
sigma and tau)