Allow configure the order used to synch tables back to postgresql

[gioman]

In a scenario where the postgresql/postgis data model has functions and triggers, then is also likely that the tables must be updated following a specific order. This also means that this #145 (comment) should be fixed first, as dbsync fails if a table has a trigger.

[wonder-sk]

The order of sync of tables should not really matter, because when applying changes, we temporarily disable triggers on tables (otherwise such triggers could further modify the database, creating inconsistent state).

[SrNetoChan]

Hi @wonder-sk! How about foreign keys, are those disabled too? Many times one table values depend on other tables rows that may not exist yet.

[wonder-sk]

Foreign keys are currently not disabled - and indeed this could lead to db-sync errors if the changes are in the diff in the wrong order. This is similar to MerginMaps/geodiff#210 (which concerns geopackages / sqlite driver). In PostgreSQL it should be possible to defer constraint checks to the end of the transaction.