Create a task that loads required thesauri automatically

[etj]

Some thesauri, e.g. for the i18n labels, needs to be atuomatically loaded at boot time.
Unlike the fixtures, theusaurs may be loaded over and over, since there's an update mechanism that only loads the deltas.

This task will also be used in projects, where mandatory custom thesauri are often used.

The thesaurus command (issue , doc) should be used, using the load --action update logic.