Remove common_currency model entirely

- A lot of views / pages / etc needed to be updated too
- Now uses django-money fields entirely
- Create a manual rate exchange backend (needs more work!)

InvenTree/company/tests.py

@@ -6,6 +6,8 @@ from .models import Company, Contact, SupplierPart
 from .models import rename_company_image
 from part.models import Part
 
+from InvenTree.exchange import InvenTreeManualExchangeBackend
+from djmoney.contrib.exchange.models import Rate
 
 class CompanySimpleTest(TestCase):
 
@@ -32,6 +34,14 @@ class CompanySimpleTest(TestCase):
         self.zerglphs = SupplierPart.objects.get(SKU='ZERGLPHS')
         self.zergm312 = SupplierPart.objects.get(SKU='ZERGM312')
 
+        InvenTreeManualExchangeBackend().update_rates()
+
+        Rate.objects.create(
+            currency='AUD',
+            value='1.35',
+            backend_id='inventree',
+        )
+
     def test_company_model(self):
         c = Company.objects.get(name='ABC Co.')
         self.assertEqual(c.name, 'ABC Co.')