Touristic content additions

**TODO**

* [x] Respect table names conventions (t_r_ : relation, t_b_ : bibliotheque, t_t_: table)
* [ ] Serializer tests for category types
* [x] Serializer for list of content types
* [x] Fixtures values
* [x] Fixtures pictograms
* [x] Contents/Events for topologies with buffer
* [x] Contents/Event for contents/events with buffer
* [x] POIs/Treks for contents/events
* [x] detail fragment with events / contents
* [x] Add regex/widgets/placeholders/help texts in content/events forms
* [x] Chosen for m2m in content/events forms

**EXTRA**

* [ ] Bug textpath on polygons
* [x] Combobox in list page
* [x] Preselect category in form when coming from filtered list
* [x] Geometry type in category
* [x] Add events / contents in maps layer switcher
* [x] Tourism filters, by city, etc.
* [x] Filter types by category in touristic content list filter

Reversing touristic content/event views fails when experimental features are disabled. This is why navigation tests fail.