Use black as formatter for python files

Update Custom Field logic for Netbox v2.10.x

Fixed IP address creation for Netbox 2.9

Add function to load YAML files ...

This commit starts to remove some code redundancy from the startup
scripts for easier maintenance.

Update IP Initializer for Netbox 2.7 ...

The ip address 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 ip_addresses.yml
file as follows:

- Make sure the status is written in lower case.

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

Added newline and breaks.

Fixed further requirements.

Fixed aesthetics.