Changing default merge strategies for options sync.

Anything related to posts now uses `destructive-import`. This is because we could otherwise end up with a ton of orphaned rows in the database related to posts. This is also because it is not typically the speicifc posts that are important in a quickstart install, so we just import the new ones.

Everything else uses `merge-import`. This is so that existing options and users remain in place, and only get updated by the new values. By default keys that exist in both databases are left untouched which is important because otherwise some options can get royally destroyed renderring quickstart inoperable. Unless we eventually build a blacklist of options to never update this should remain as is.