Show form elements for templates and folders

This commit adds:
- checkboxes to let you select a template or folder
- radio buttons to let you select where to move those template(s) and/or
  folder(s) to

It only does the `get` part of this work; handling the `post` and
calling API will be done in a subsequent commit.

app/assets/stylesheets/components/message.scss

@@ -23,3 +23,18 @@
 #template-list {
   margin-top: $gutter;
 }
+
+.template-list-item,
+.template-list-item-with-checkbox {
+  position: relative;
+}
+
+.template-list-item-with-checkbox {
+
+  padding-left: $gutter * 2;
+
+  .multiple-choice {
+    position: absolute;
+    left: 0;
+  }
+}