Clean up rights API

Remove getPersistedRules from the RightReader API, and refactor existing code so that it does not rely on this function anymore.
The way to get persisted rules should be by using the getRules method with the boolean parameter withImplied set to false.

Also improve health of existing code:

• Change variable names from abbreviation to full name
• Make every function have 1 and only 1 return
• Use boolean primitive in function parameters
• Use Collection.emptyList() instead of explicitly creating a new empty list