Instance pulling WIP

NC-202
Merge branch 'develop' into feature/nc-202

Conflicts:
	nodeconductor/iaas/models.py
Make Instance belong to CPM

Now it directly points to cloud_project_membership
rather then two separate cloud and project fields.

The public API is still intact.

NC-202
Clean up commented-out remnants

NC-202
Fix admin interface for Instance list

NC-202
Make instance's key_fingerprint optional

NC-202
Fix and document filtering for instances and services

NC-202
Merge branch 'feature/nc-202' into 'develop'

Fixes for cloud + project to cpm migration for instance, NC-202

* Fix Django admin for Instance list
* Fix filtering and ordering for instance list and service list
* Improve API for filtering and ordering, deprecate old parameter names
* Update API docs for instance and service lists