improved history for slices

[osmisto]

I think the current history is too simple to be usefull. The goal is to allow contributor overview important comments and changes in one sight.

So on first load it should not show all events and comments, but only:

• pinned comments (need ability to pin important like bing offset). They should be on top always.
• last few comments and status changes. Only amount that can be shown without scrolling.
• "reserved by" if the slice is currently reserved

and the link to load and show all history.