Support QGIS 3.16

[Gustry]

It's a work in progress :

• Check all processing.gui.wrappers_postgis.ConnectionWidgetWrapper
  • Import covadis
  • export covadis
  • load layers
  • load styles
  • configure
  • create
  • upgrade
• Check all processing.gui.wrappers_postgis.SchemaWidgetWrapper, ticket lié Forcer le schéma ou non #59
  • export covadis
  • import covadis
  • load layers
  • load styles
• Check all processing.gui.wrappers_postgis.TableWidgetWrapper
  • import covadis
• Remove all fetch_data_from_sql_query which is using old DB Manager code
  • upgrade
• Remove all from processing.tools.postgis import uri_from_name
  • export covadis
  • load layers
  • import covadis

[Gustry]

@rldhont The only remaining algorithm broken is the upgrade one, I got issues with it, still related to #91. Strange.

Even if you are running QGIS 3.10, pull and try latest master for your dev.

Commits : d8b7012 eced0bf a81338d

[Gustry]

Last commit bfebfee

The ticket can now be closed. I will give it a try again manually.