Enable column transitions with a conditional model

[fsaad]

Currently disabled, need to ensure the following cases

Invariants to maintain

• Conditional models are never initialized into singletons.
• Conditional models are not proposed to move into singletons in the column CRP.
• Conditionals models are not isolated (become singletons) when columns in their Views are being transitioned.

Correctly computing the transition probability

• When an unconditional column is proposed to a View with a conditional column, need to compute both the marginal probability of the unconditional column under the View clustering and the delta in marginal logp of the conditional column, retraining given the proposal.

[fsaad]

Because dimensionality change of conditional model, my concern is that the "trivial" Gibbs sampler is not going to be reversible and we need RJ-MCMC algortihm for which interface design is not straightforward as of now.

[fsaad]

This is actually a research project.