[appserver-io/doppelgaenger] DbC errors do not produce a readable output

[wick-ed]

Currently the output of any DbC error has a very technical style and exposes application internals.
This has to be changed.

UAC:

• Output MUST be able to conceal technical internals
• Output MUST be able to convey domain specific meaning (e.g. invalid email address format)
• Conditions COULD be more domain logic specific
• Additional syntax MUST be applied to the mop PSR

See for example: https://github.com/hoaproject/Realdom

[wick-ed]

Feature has been implemented, PSR still needs adaption though