Complete V3 design for feature parity with lib/

[ralflang]

• Detect missing features and aspects in the src/V3 implementation.
• Find modern, strongly typed equivalents to lib/ paradigms, potentially using named parameters and defaults.
• Implement missing aspects
• Update unit tests to cover the new design. Expectations should be equivalent with lib/ (equivalent input yields equivalent output)

[amulet1]

There are few things we need to make it happen:

• Some simple V3 on/off switch to make it easy to test things and revert back easily if the issue is detected. Possibly some temporary config parameter. Any suggestions? Once we agree on the "switch", just a few changes will be needed to use V3 classes automatically (with a few exceptions).
• Embed code from VarRenderer classes into V3 classes (does not delay transition to V3 classes)
• Update interfaces, improve code
• Tests

[amulet1]

@ralflang Please advise on the "V3 on/off switch".

[ralflang]

I think we need a form switch either at application level or at horde-wide level.

[amulet1]

Maybe a global setting "Use experimental V3 Form classes"?

And possibly another checkbox to "Allow users to override" (and then a corresponding user preference). This way it can be tested in multi-user environment, and could be easily enabled/disabled globally or only for specific users.