Add keywords.add_unique_keywords function.
* Add test unit.
* Add licences notes to src files.
* Add synonymous support.
* Add "new keyword" enlighting, maybe with link to keyword editing.
* Add similar keywords suggestions. Otherly said: "Bookmarks which have
X keywords also have this keywords. May be some frequency filter will
be needed.
* Selection based bookmarks editions.
* Used SQL sequence instead of the db_sequence table.
* Add CSS.
* Add Search capabilities.
* Add default (dynamic?) tree expansion using colltags.
* Add XBel Export.
* Add support for icons.
* Add modified time.
* Add access/check time.
* Add user session support.
* Better unicode handling.
* More user preferences.
* Clean up of all the code. This is a real mess currently!
* Optimization of some code part.