improved tag filter (many) and support for adding tags to result-items.

Fixes which came unmentioned in last commit:
- fixed missing workspace assignments for our topictypes
- changed service namespace from /eduzen to /notes
- added piwik tracking code for research.eduzen.tu-berlin.de

Improvements:
- build up a relative tag-filter (tags in relation to the remaining resultset)
- revised, unified method signatures

ToDo:
- enable editing and deletion of single resources

Pending:
- allow users to manipulate the tag-filter per item
- enable pasing of HTML sources into resource a field

Pending: mathjax-rendering to be fixed.