Use multi-file upload for "images" field

Closes #62

apps/files/forms.py

@@ -1,9 +1,14 @@
 from django import forms
 
-from .models import File
+from .models import File, ImageFile
 
 
 class FileForm(forms.ModelForm):
     class Meta:
         model = File
         exclude = ['user',]
+
+class ImageFileForm(forms.ModelForm):
+    class Meta:
+        model = ImageFile
+        exclude = ['user',]