Hiding field when there is only one choice

Closes #67

ippisite/ippidb/forms.py

@@ -424,6 +424,7 @@ class PpiModelForm(ModelForm):
             self.fields["symmetry"].queryset = symmetry
             if symmetry.count() == 1:
                 self.fields["symmetry"].initial = symmetry.first()
+                self.fields["symmetry"].widget = forms.HiddenInput()
 
     def full_clean(self):
         super().full_clean()