Refactor ValidatedSoftwareLCM and the software helper logic.

[progala]

Note This PR introduces schema changes.

Refactored the ValidatedSoftwareLCM model and filters, forms etc. that reference it.

Moved helper functions for working with SoftwareLCM and ValidatedSoftwareLCM objects to software module.

List of changes:

• ValidatedSoftwareLCM now allows assignment to multiple objects.
• ValidatedSoftwareLCM can now be assigned to:
  • devices
  • device types
  • device roles (new)
  • inventory items
  • tags applied to any of the above (new)
• Re-worked CSV import/export for ValidatedSoftwareLCM
• Refactored out helper logic computing SoftwareLCM and ValidatedSoftwareLCM related objects.
• Updates to view templates.
• Added valid filter to ValidatedSoftwareLCMFilterSet
• Change ordering of the SoftwareLCM objects.
• Removed ValidatedSoftwareLCM content template for the DeviceType.
• ValidatedSoftwareLCM can now return queryset tailored to a given object with get_for_object.

[dgarros]

Great work @progala

[dgarros]

Would it make sense to convert get_validated_software_qs into a queryset class for ValidatedSoftwareLCM
This would allow us to have something like that

device = Device.objects.get(XXX)
validated_software = ValidatedSoftwareLCM.objects.get_for_model(device)

it's easier than it look to implement
We just need to create a new class

class ValidatedSoftwareLCMQuerySet(RestrictedQuerySet):
    """Queryset for `ValidatedSoftwareLCM` objects."""

    def get_for_object(self, obj):
        """
        Return all `ValidatedSoftwareLCM` assigned to the given object.
        """
       if obj is of type Device:
             do this
       else:
             do that

       [..]

class ValidatedSoftwareLCM([..]):
      objects = ValidatedSoftwareLCMQuerySet.as_manager()

Here is an example https://github.com/nautobot/nautobot/pull/1047/files#diff-01ee6b16cefc4c5378473d290760c32b2507d31249d3df90972f4dca6a93d33aR16

[progala]

I made an attempt at implementing that and moved a few things around. Seems to work well.

@dgarros @josh5276 @jvanderaa Could you please review and we could hopefully merge it soon.

[dgarros]

LGTM, great work @progala