Fix handling of prefixed Asset IDs and sorting of the asset list (#382)

* FIX: Remove misleading admin site title

* Moved across assets_id sorting to use proper numeric values. Also mofifies SQL command to find free asset IDs so that it works on postgres.

* Changed generateSampleAssetsData.py to include prefices on some cables.

* Fixed pep8

* Fixed missed migration

* Ensured hidden asset fields are completed on every database write

* CMULTI is a thing, and therefore a max prefix length of 5 cannot be a thing

assets/forms.py

@@ -7,6 +7,7 @@ class AssetForm(forms.ModelForm):
     class Meta:
         model = models.Asset
         fields = '__all__'
+        exclude = ['asset_id_prefix', 'asset_id_number']
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)