* feature/system-cron: (67 commits) [feature/system-cron] More tests for cron manager. [feature/system-cron] Added documentation for cron manager constructor. [feature/system-cron] Remove an unecessary assignment and an unecessary comment [feature/system-cron] Clarify comments about flush() call in cron. [feature/system-cron] preg_match returns int so cast to bool, fix comment [feature/system-cron] Rename lock() to acquire and unlock() to release. [feature/system-cron] Cache cron's task names. [feature/system-cron] Use a RecursiveDirectoryIterator instead of readdir. [feature/system-cron] Add array type hints if appropriate and remove globals. [feature/system-cron] Make use of the new config class in locks. [feature/system-cron] Fix duplicate instantiation of class loader in tests. [feature/system-cron] Abstract the database locking mechanism out of cron. [feature/system-cron] Move tests to phpunit.xml and always load class loader [feature/system-cron] Basic tests for cron manager. [feature/system-cron] Added @param/@return documentation [feature/system-cron] Add phpDoc documentation for everything else. [feature/system-cron] Cast result in cron_manager::is_valid_name() to bool. [feature/system-cron] Add phpDoc documentation for phpbb_cron_manager class. [feature/system-cron] Add phpDoc documentation for phpbb_cron_lock class. [feature/system-cron] Adjust SQL query style to follow coding guidelines. ...