Notification of string changes

Author: Damyon Wiese
MDL-58128 oauth2: Add a scheduled task for refresh
We need to make sure our refresh tokens do not expire. We run a scheduled
task to update the refresh token once per hour.

Part of MDL-58220


http://git.moodle.org/gw?p=moodle.git;a=commit;h=d247a63dfa49661c00499be26b352009ef3d4ef0
http://github.com/moodle/moodle/commit/d247a63dfa49661c00499be26b352009ef3d4ef0

+ 3.3 en [oauthrefreshtokenexpired,core_admin]
+ 3.3 en [oauthrefreshtokenexpiredshort,core_admin]
+ 3.3 en [taskrefreshoauthtokens,core_admin]