Static cache takes from 20 - 60 seconds to regenerate on pages with many dependencies, so it't better off being done by a cronjob.

This patch includes support for setting staticcache.ini [CacheSettings] CronjobCacheClear=enabled.
This makes eZZtaticCache::executeActions() insert the actions to ezpending_actions with action='static_store'.
The cronjob for regenerating the cache is also included.

This enchantment may have dependencies with #010855 and #010854!