Cache speech delivery tagging

This is one of the main culprits for the slow loading of the speech
forms. Slight tweaks were made to the cache digest calculations for
ministerial role appointments to scope it to just ministerial roles to
distinguish it from the digest for all role appointments.
Detailed guides factory generates unique titles

Makes comparing editions based on their title easier out of the box.
Cache related detailed guide fields

This should result in a big performance improvement on the detailed
guides form as loading all active detailed detailed guides to generate
this select is painfully slow.
Cache related statistical data set fields

Only used on publications, but still a fairly slow select to generate.
Use edition documents to generate cache digests

Using editions to generate the cache digests is incredibly inefficient
because there will be multiple editions per-document. By making sure
that the parent document of an edition is "touch"ed after any update, we
can use the Document to generate the cache digest much more efficiently.
Cache related worldwide priority fields
Get rid of "magic" helper method

This helper existed to get around the fact that the dynamic ActiveRecord
related_policy_ids method would not return any ids for non-persisted
records that had been assigned their related policies using the
related_policy_ids= method. By overriding the method to go through the
underlying association that links editions to policy documents, we can
ensure that we get the expected ids for both persisted and non-persisted
records.