Add IP mapping model and serializer

nc-59
Add ip mapping factory and tests

nc-59
Add ip mapping filter

nc-59
Extended IP mappings with project group links

- NC-59
Typo
Add tests for filtering ip mappings

nc-59
add documentation for ip mapping and extend createsampledata

nc-59
Move IP mapping from structure to cloud app

nc-59
Change ip mapping private and public fields

nc-59
Merge branch 'develop' into feature/nc-59

Conflicts:
	docs/api/api.rst
	nodeconductor/testdata/management/commands/createsampledata.py
Change test case to transactional
Fix typos and remove duplication

nc-59
Merge branch 'feature/nc-59' into 'develop'

Feature/nc 59