Use multi-file upload for "images" field

Closes #62

apps/map/models.py

@@ -442,25 +442,12 @@ class CaseStudy(models.Model):
         blank=True
     )
 
-    # 1.15.1
-    image = models.ImageField(
-        verbose_name=_("Image")
-    )
-
-    # 1.15.2
-    image_caption = models.CharField(
-        verbose_name=_("Image caption"),
-        max_length=240,
-        default=None,
-        null=True,
-    )
-
-    # 1.15.3
-    image_credit = models.CharField(
-        verbose_name=_("Image credit(s)"),
-        max_length=240,
-        default=None,
-        null=True,
+    # 1.15.1, 1.15.2, 1.15.3
+    images = models.ManyToManyField(
+        'files.ImageFile',
+        related_name='image_for',
+        verbose_name=_("Images"),
+        blank=True
     )
 
     # 1.16.1