[FIX] Add description Scientific Programme PDF

- Closes #1350
[IMP] support custom converters in build_url()
[IMP] Add some __repr__ methods
[MIN] Interesting events. Still very much WIP
[IMP] Add task to update category suggestion info
[FIX] CategoryDisplay UH when used w/o target param

e.g. in the http api when fossilizing
[IMP] Show suggestions in the dashboard
[FIX] Missing >
[FIX] Unusuggest category when removing it from favs
[MIN] Python 2.6 collections.Counter