Add association rules

New rules :
- A gite can not be linked to a route
- A parking can not be linked to a route if a main/sub parking is already linked to it
- A sub site can not be linked to more than one main site
- A site can not be linked to more than one summit
- A summit can not be linked to a sub site
- A sub summit can not be linked to more than one main summit
- A sub parking can not be linked to more than one main parking