Feature/managing plans overfills

## Features

- **Topic count**, **node count per topic** and **plan limitations** added to `User Resource`
- Show a message at the top of the page everywhere saying you get near the plan limitation, if you do.  
  Messages are in `app/detective/templates/partials/home.plan-overfill-messages/`
- Show a message instead of the contribution form if the topic owner plan is overfilled
- Allows directories for ordering html partial files 529aacb

## TODO

- [x] Check if the plan is overfilled on the back-end side before saving a new model.  
  where ? Here https://github.com/jplusplus/detective.io/blob/develop/app/detective/individual.py#L36  
code 500

## FIXME

- [ ] Topic.entities_count() is still very expensive and doesn't care about old model which are no more in the ontology.