Break ties for best entitlement group by number of ents

Break ties on number of entitlements, rather than our old
agnostic approach.

prefer subscriptions that match socket count
Much better pool comparator for sockets
pick groups better
use priority for other attributes
add tests
add some comments on new autobind logic
Rev rules again
Merge pull request #616 from candlepin/ckozak/better_autobind

Ckozak/better autobind