* FEATURE: Limit the amount of assigned topics an user can have.
* Do not enfore the limit when self-assigning
* Avoid computing the query when self-assigning. Do not count self-assigns when enforcing the limit
* 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