[multi-sources-removal] Turn ConnectionsSet into simpler ConnectionWrapper
also, SqliteConnectionWrapper becomes a subclass. This is allowed since
now ConnectionsSet responsability has been reduced to handling the system
source only.
This changeset also:
* drops useless cnxset_set / check_connection api
* deprecates former .source / .connection / container api
but it renames neither the session's cnxset attribute, nor the related
repository method.
Related to #2919300
CSS Coding Standards
--------------------
(Draft, to be continued)
:Naming: camelCase
Indentation rules
~~~~~~~~~~~~~~~~~
- 2 espaces avant les propriétés
- pas d'espace avant les ":", un espace après
- 1 seul espace entre les différentes valeurs pour une même propriété
Documentation
~~~~~~~~~~~~~
Please keep rules semantically linked grouped together, with a comment about
what they are for.
Recommendation
~~~~~~~~~~~~~~
- Try to use existing classes rather than introduce new ones
- Keep things as simple as possible while in the framework
- Think about later customization by application
- Avoid introducing a new CSS file for a few lines of CSS, at least while the
framework doesn't include packing functionalities