server-handlers, errorhandling configurable

[TobiasNickel]

last week I already proposed an update for the handler-service. that will allow a better error-handling.
by allowing afterfilters to send a reasonable result to the client
and catching sync errors in the handler, to not let them get catched on the mail-service but be handled by afterfilters.

I was told, the change should be configurable. so I used app.get('enfrceHandlerResponse')
and app.get('catchHandlerErrors') to enable both features manually in app.js.

[TobiasNickel]

will you take it?