Implement Soft Conditioning

[zenna]

Integrate soft conditioning. A lot of the machinery behind this is now in SoftPredicates.jl. The tricky parts will be:

• How do soft predicates integrate with log likelihoods?
• Can SoftPredicates use some tagging infrastructure?

Dependencies:

• Basic MH algorithm

[zenna]

Unclear exactly what this means. Could be:

1. Integrate softconditions with logdpf
2. Just actually support sampling with soft conditions. I guess there's a deeper question of what should be the interface to temperature controls and MH