improve exception handling

Possible exceptions should always get carried through the functions to the calling function in the controller.
The view already has a method for exception displayment, but could use some rework as the normal user isnt interested in the stacktrace (but still wants to be notified if things go south!)

Start by locating the controller functions that can raise exceptions and the view method responsible for displaying them. Trace how exceptions currently move between these layers and identify the existing stack-trace output. Done means exceptions reach the calling controller and users are notified without seeing stack traces.

Written by the indexing model from the issue text.