Fix migrations failing when no statuses exist and other various migrations fixes

[gsnider2195]

Closes #272

• In migrations only create statuses that are configured in the plugin settings default_status and allowed_status if they don't already exist. Associate all firewall models that have a status field to these statuses through the content_types field.
• In database_ready signal, create statuses that are configured in the plugin settings default_status and allowed_status. Associate all firewall models that have a status field to these statuses through the content_types field.
• In database_ready signal, associate all firewall models that have a status field to the Active, Staged and Decommissioned statuses. Skips any of these statuses if they don't already exist. This logic was removed from multiple migrations

[smk4664]

This looks great and resolves the issue with migrations.