[FIX] end date calculation
[FIX] end date calculation

A failed task must not end this week. Thus, we need to change the end
date for a task if its reports say it failed.
Furthermore, a task that already succeeded may end this week. We also
change its end date accordingly.
An already finished task may become red again. In this case it needs to
be reopened by setting its end date accordingly.
This patch adds all three end date modifications.

tapper/Tapper-Testplan