Do not look for adhocracy module on every request

Previously, our translation mechanism went looking for the location of the adhocracy module (in order to later find the i18n file) on every request, causing about half of all per-request I/O calls (typically cached, but a context switch nontheless).
We can simply look the location in userspace entirely after reading it once.
This was found during hhucn/adhocracy.hhu_theme#401