[BUGFIX] Do not cache URLs containing session IDs

To reduce the amount of URLs stored in the cache the store command
will only be executed when not Frontend user is logged in and
no session information is appended to the URL.
[FEATURE] Background process PDF generation

Since there seem to be some problems when the PDF generation process
is controlled by PHP it is now also possible to run the process
in the background by using the new "runInBackground" configuration.