Reporting: fix filter urls

The regex match for the filter urls were to strict. They disallowed
some charaters, that are valid in group names and so the django reverse
mechanism for building urls failed.
Reporting: better exception handling

Try to keep the try-except-blocks as small as possible.
Merge branch 'reporting-fix-filter' of https://github.com/AlexanderS/bcfg2 into maint