populateContentModel: Invalidate content model and revision cache

populateContentModel: Invalidate content model and revision cache

The cache is computed from both the default values and the DB.

If someone visits the page when the wrong default value is there,
it will be cached.

When we populate the DB with the correct value (usually in preparation
for changing the namespace default), we need to invalidate the
potentially broken cache.

Change-Id: I995c0d9fdec529a456762571d5406d0bd0d33aed