Update Custom Field logic for Netbox v2.10.x

Update Rack Initializer for Netbox 2.7 ...

The rack database model has changed in Netbox 2.7.
Therefore the initializer code, that was used before, broke.
As a user, you will need to update your racks.yml file as follows:

- Rack types must match one of the 5 rack types given, e.g.
  '4-post-cabinet'.
- Rack width must match one of the 2 rack widths given, i.e. '19' or
  '23'.

See the diff of this commit for further information how this is meant.

Add rack group initialiser ...

Fixes #192

Signed-off-by: Jeroen Simonetti <[email protected]>

Fix initializers

Add rack seeds