Global reminder bot

This is a bot (by Leaderbot) that reminds users when their rights are to expire, based on phab:T370842. This is currently opt-in for a wiki, but the plan is to make this opt-out in due course.

• The bot will remind users once (and only once) when their rights are due to expire in a week's time or less. This may be tweaked later on.
• To exclude a user from this bot, go to Exclusion. This bot does not respect any other form of opt-out preference and is not exclusion-compliant.
• Default configuration files are stored in /global (this also includes data for global rights).
• Local (i.e, for a certain wiki) configuration files are stored as a subpage by database name. For enwiki, this would be /enwiki and /frwiki for frwiki. Should an opt-in wiki not have a local configuration file, the global details will be used.
• The internal database is at /database and should normally not be modified.
• Anyone with "WMF" as part of their username is automatically excluded.