Add partner familiarity bias

[brettonw]

Add the ability for an atom to elect not to interact because they aren't familiar with a new potential partner. This can take one of two forms:

• Allow atoms to keep a number of slots for partners, add a probability that those partners are allowed to interact, and a probability that non-partners are allowed to interact, also allow for replacement of the known partners. So this could be used to model monogamy, or limited polyamory.
• Keep a familiarity measure parameterized as the number of interactions between this atom and a potential partner, so that it's less likely to result in an interaction the first time two atoms interact, but the likelihood increases with each subsequent potential interaction.