Don't transform zone labels to uppercase by default.

This is to ensure compatibility with screen readers: When transforming
text to uppercase via CSS, (some) screen readers spell out individual
letters of zone labels (instead of reading labels as a sequence of words).

cf. https://github.com/edx-solutions/xblock-drag-and-drop-v2/pull/34#issuecomment-174032333

drag_and_drop_v2/public/css/drag_and_drop.css

@@ -250,7 +250,6 @@
     font-size: 16px;
     font-weight: bold;
     text-align: center;
-    text-transform: uppercase;
     margin-top: auto;
     margin-bottom: auto;
 }

drag_and_drop_v2/public/css/drag_and_drop_edit.css

@@ -45,7 +45,6 @@
     font-size: 16px;
     font-weight: bold;
     text-align: center;
-    text-transform: uppercase;
     margin-top: auto;
     margin-bottom: auto;
 }

tests/integration/test_interaction.py

@@ -397,13 +397,13 @@ class EventsFiredTest(DefaultDataTestMixin, InteractionTestBase, BaseIntegration
                 'is_correct': True,
                 'is_correct_location': True,
                 'item_id': 0,
-                'location': u'The Top Zone',
+                'location': TOP_ZONE_TITLE,
             },
         },
         {
             'name': 'edx.drag_and_drop_v2.feedback.opened',
             'data': {
-                'content': u'Correct! This one belongs to The Top Zone.',
+                'content': ITEM_CORRECT_FEEDBACK.format(zone=TOP_ZONE_TITLE),
                 'truncated': False,
             },
         },
@@ -411,7 +411,7 @@ class EventsFiredTest(DefaultDataTestMixin, InteractionTestBase, BaseIntegration
             'name': 'edx.drag_and_drop_v2.feedback.closed',
             'data': {
                 'manually': False,
-                'content': u'Correct! This one belongs to The Top Zone.',
+                'content': ITEM_CORRECT_FEEDBACK.format(zone=TOP_ZONE_TITLE),
                 'truncated': False,
             },
         },