Fixes for codemirror in sources modal

- Allows for max height
 - Override GeoJSON data when changing type

src/styles/index.scss

@@ -37,6 +37,7 @@ $toolbar-offset: 0;
 @import 'zoomproperty';
 @import 'popup';
 @import 'map';
+@import 'codemirror';
 @import 'react-collapse';
 @import 'react-codemirror';