* FIX: Skip enqueuing reminders if no groups are allowed.
With an empty SiteSetting.assign_allowed_on_groups, it used to generate
an invalid query containing "group_users.group_id IN ()".
* Feature: Allow assign on groups
* Use type: group_list option
* Track group changes and update the setting accordingly. Restrict reminders frequency to assign allowed users instead of staff
* FEATURE: Users can override reminders frequency
* Changes:
- Avoid creating a user custom field when the used didn't override the frequency
- Sanitize frequency value using coercion
- Minor fixes
* Sanitize query and user query single
* FEATURE: Remind users of assigned tasks.
* User an user custom field instead of adding a new column
* Improve tests. fix assigns count and display oldest assigned topics correctly. Do not remind about recently assigned tasks
Dan Ungureanu
Sam Saffron
Roman Rizzi
Guo Xiang Tan