Handle the case of two conditional component models in a View

[fsaad]

As it stands, conditional component models are created by using View.update_cctype, and the allowed inference operator are everything except column transitions.

When a user invokes View.update_cctype(a) and then View.update_cctype(b):

• The first conditional component model a must be re-trained, no longer taking a as an input.
• Must ensure the View contains at least 1 conditional model.

A crash stub for this case exists in https://github.com/probcomp/gpmcc/blob/master/tests/test_lw_rf.py#L42-L43