move avail accounts mixin to account mixins file. Add avail accounts mixin to Connection viewsets

qrtr_account/mixins.py

@@ -0,0 +1,15 @@
+from django.db.models import Q
+from qrtr_account.models import Account
+
+
+class OwnedAccountsMixin():
+    """Mixin to help getting a list of accounts
+    the given user is authorized to see
+    """
+
+    def accessible_accounts(self):
+        usr = self.request.user
+        accs = Account.objects.filter(Q(owner=usr) |
+                                      Q(id__in=usr.admin_accounts.all().values_list('id')) |
+                                      Q(id__in=usr.view_accounts.all().values_list('id')))
+        return accs