Drop NetworkSegment model

NC-233
Drop purchase model and related stuff

NC-233
Make CharFields non-nullable

NC-233
Add core initial migrations

NC-233
Add structure initial migrations

NC-233
Add iaas initial migrations

NC-233
Add backup initial migrations

NC-233
Add ldapsync initial migrations

NC-233
Merge branch 'feature/nc-233' into 'develop'

Add initial database migrations, NC-233