Decouple UserWarning from domain-specific warnings

Examples of domain specific warnings in view.py module:

raise_exception(par, UserWarning, 'parameter value is not computed yet')

The result is two lines domain-specific message.

Examples of UserWarning:

/mnt/data/ubuntu/work/vre-language/src/virtmat/language/cli/run_model.py:125: UserWarning: argument autorun will be ignored in instant mode
  warnings.warn(f'argument {attr_} {bstr_}')

The latter type of messages should be done as the first ones.