Conflict resolution logic is not very optimized for multi modifications

The use case is the following: two instances cannot communicate with each other and both modify the same document during that time (at least one of the instance doing several modifications).

When the connection is restored, there are various problems:

• optimization: too much conflict resolution
  • both instances will have and resolve similar conflicts and resend complete version, could be "fixed" by doing conflict resolution only on the document owner (requires REPLICAT-7)
  • each version will cause a conflict merge because for each version the other instance will notice that the version/date does not match what's expected, which will trigger a conflict resolution (2 new versions and a resend of the complete document to the other instance).
    Hard to do much about this because there is not much room to store hidden custom replication related metadata in the XWiki history.
• bug: the 3 ways merge might be done from the wrong common version: REPLICAT-57