Reduce inconsistencies in tr()-Strings provided for
QActions that act on a current <something> (mostly files) by
introducing a ParameterAction class that takes the tr()-Strings
at construction time and provides a setParameter(QString) slot,
allows for setting that parameter or an empty string, which
will cause the displayed text to be updated.
Details: Use a global model for nicknames that is shared by all dialogs to solve the updating problems. Make p4 plugin submit work again. Force a submit prompt in case of shutdown or editor close (as opposed to user clickling on "Submit").
