Feature + Bugfix : Fix CGI graphs

Feature + Bugfix : Fix CGI graphs.
If you use cgi to generate graphs and you somehow broke dynazoom/ graph generation,
this will change the permissions so apache2 can read and write graphs and data.

You can break the permissions by running "munin-check --fix-permissions" 
Munin is not aware which process generates the graphs or what permissions it should have.

I suppose an alternative solution would be to add www-data/apache2 to the munin group - but the ACLs that come with munin are rather flaky.