Better grouping of activities

Fix #2, #1, #12 

* [x] the full path should only be shown for each individual file. Hovering over one file should show that files’ full path (using a tipsy tooltip please).
* [x] when you click the »5 more« notice, expand to show those other file names as well. You can then also hover the other filenames for the full path.
* [x] leave out the first slash in the path, it looks strange to non-technical people

:construction: