Added missing model response factory.
Improve conflict solver to take into account the initial documents.

This documents have equal bodies but different revisions. In such case
we should just resort to the db winner strategy.
Integrity agent checks for conflicts on startup and intitiates the cleanup.
Change integrity agent to use only one alert with a fixed name.

Previously it was using one per each unsolvable documents which was a
straight road to a disaster.
Merge branch 'master' into release-0.27.x