check for qualifier consistency when returning VCCs from controller

[Dierk]

Attributes with the same qualifier must always have the same value. However, when synchronization gets out of step, a controller might return a list of ValueChangedCommands that set attributes with the same qualifier to different values as detected by @DieterHolz. This will inevitably lead to oscillation.

Solution idea: in the server adapter, before applying the codec, clean the list from all offending VCCs. Question: which on counts: first or last?