Aa-forum

Added

- "Show all unread topics" and "Mark all topics as read" buttons above the category
list in forum index
- "Mark all topics as read" in the unread topics view above and below the board list
- More logging
- Access check if when someone tries to reply to a topic, they lost access to while
viewing

Removed

- Arbitrary `user_has_access` function from `Message` model

Added

- Unread topics functionality to list all unread topics for the current user

Added

- Child boards (1 Level). Child boards will inherit their access restrictions from
their parents.

Fixed

- [Bootstrap] CSS class moved to the right element

Changed

- CKEditor config changed to prevent possible collisions in static files (see
[README.md] for details)

Added

- Ability to change the subject of the topic (User needs to be the original poster or
forum admin to change a topic's subject)

Changed

- Link to a message now has the full path (category, board and topic) in its URL

Fixed

- When the first message is deleted, the topic will be deleted as well. This is to
prevent having topics with replies to a message that does no longer exist.