bugs:310
log events into a system journal
config table settings
* ##log_purge_time##
* Remove event log over a given number of days.
* ##maint_last_log##
* timestamp of last maintenance -> purge
* ##log_default_show##
* The minimum priority events displayed in the log by default in the admin panel
* ##log_level##
* The minimum priority of the events recorded in the log
Log event
%%
// e.g.
$this->log(1, $engine->_t('LogAdminLogout', SYSTEM_LANG));
%%
* ++log messages should use the config default language in the ##_t## function else we got mixed language log messages++
===Logged actions: ===
====1 critical====
- admin action, object deletion, suspected hacking attempt
====2 highest====
- locking, acl change, unsuccessful user login
====3 high====
- page renaming/moving/splitting/merging, user password change/reminder, successful user login
====4 medium====
- page creation (settings change), poll action, file upload, pm sending, user registration and email activation, page ownership claim
====5 low====
- comment posting, user logout
====6 lowest====
- page edit, user settings update
====7 debugging ====
- everything, where logging is necessary