fixes #6529 allow to define IP suggestion per subnet

fixes #1814 - converts sp_* attributes into a BMC interface class

this patch also includes the following

• added a new interfaces table, and STI objects to represent a NIC, BMC, Managed
  and a bootable interface.
• refactored DHCP/DNS orchestation code, so they can work on the...

This commit adds most of the functionality required for API v1

The overall goal was to extract the existing JSON response
overall controllers, and to move them to a seperate name space.

• documentation was added to all requests (available under /apidoc)...

added dns_id, dhcp_id, tft_ip attributes even though they are nested as children to be consistent with current api

Subnets API