Make all REST resource relations render in a common way.

Each entity is render with a pair of fields like this:

"project": "http://exampe.com/api/projects/uuid1/",
"project_name": "Project 1",

NC-108
Expose Flavor's fields to REST resource

NC-74
Add get_related_paths to InstanceSerializer

NC-108
Merge branch 'feature/nc-108' into 'develop'

Expose Flavor fields, generalize related resource fields, NC-108