Add Category List API resource

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Add Category List link to Project resource

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Use keywords args in CategoryCollectionRepresenter

See 34780d5f.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1637 from opf/feature/api-auxiliary-resources-category