Option to prefix ban reason with ban list name, ban entry time and local ban density

[bkil]

• Assume that you are watching multiple foreign ban lists.
• You are seeing someone being banned from your room.
• You may want to better understand why they got banned.
  • Not all moderators provide detailed reasoning to their ban rules.

Hence it would be helpful when Mjolnir bans someone from a room based on a rule, it should include as much metadata in the ban reason as possible. This includes:

• The original reason string (if it was provided)
• The ban list and/or the short code
• The time of the ban list entry
• Optionally the ban entry density in the ban list at the point of time the rule was created (i.e., how many bans were added within 1 hour and 1 day radius) This could prove to be valuable information for debugging and "forgiveness", because in case of spam waves, certain moderators are trigger happy to ban anyone entering a room.

It would be also helpful to know the original room (possibly with a link to an unredacted message just before that) where abusive behavior was practiced that led to a ban, but I understand that this information is not available in the current workflow and architecture.

[bkil]

Somewhat related: #228