Fixes for codemirror in sources modal

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

src/styles/_codemirror.scss

@@ -0,0 +1,8 @@
+.CodeMirror-lint-tooltip {
+  z-index: 2000 !important;
+}
+
+.CodeMirror-wrapper {
+  position: relative;
+  overflow: auto;
+}

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';