Activity update

With this update, we have completely rewritten the activity engine. It's now much more dynamic, fast, lightweight and adaptable.

Features:
    - Activity templates in the database, which are the base of the activity messages. Very easy to edit and create more.
    - Tags, which are hightlighted parts of the activity message. These usually point to an element, like an issue or branch.
    - Tag explorer. This tool helps to perceive the element structure of each tag. E.g. shows parent issue, parent branch etc...
    - Easy access to "active things", e.g. the things that have triggered the activity.