Remove tables Identifiers and Predicates. Simplifies DB schema and
queries a lot.
Fix CachedName saving
Reorganize rpc tests
Simplify SearchForPath by extracting methods
Only save trust step and UpdateMessagePriorities if one does not already exist
Add trustpathable predicate: bitcoin
Separate table for PrivateKeys
Merge branch 'refactor-db'. No migration, requires db reset.