Qualification workflow errors: more information

[Yuri05]

At the moment it's extremely hard to track down the error location.
E.g. for PK-Ratio plots, each error should be produced in the form:

 Error: <Error message>
 Plot: <Title of the failing plot>
 PK-Parameter: <Name of failed PK parameter>
 Group: <Caption of the failed group>
 PK-Ratio: <Nr of the failed PK-Ratio>
 Call the traceback() function or check the <location of log-error.txt> to see the full stack trace

Similiar for other plot types. It should be easily possible for the user to identify the lowest level object of a qualification plan (e.g. PK-Ratio, DDI-Ratio, etc.) of the qualification plan which causes the problem.