polished multiple choice question styles

common/lib/xmodule/xmodule/css/capa/display.scss

@@ -53,6 +53,17 @@ section.problem {
       float: left;
       border-left: 1px solid #ddd;
       padding-left: 20px;
+      margin: 20px 0;
+    }
+
+    input[type="radio"] {
+      float: left;
+      margin: 4px 8px 0 0;
+    }
+
+    text {
+      display: block;
+      margin-left: 25px;
     }
   }