Added initial thunderforest source integration

src/components/App.jsx

@@ -250,7 +250,7 @@ export default class App extends React.Component {
 
   mapRenderer() {
     const mapProps = {
-      mapStyle: style.replaceAccessToken(this.state.mapStyle, {allowFallback: true}),
+      mapStyle: style.replaceAccessTokens(this.state.mapStyle, {allowFallback: true}),
       onDataChange: (e) => {
         this.layerWatcher.analyzeMap(e.map)
         this.fetchSources();

src/components/modals/ExportModal.jsx

@@ -50,7 +50,7 @@ class Gist extends React.Component {
     const mapboxToken = (this.props.mapStyle.metadata || {})['maputnik:mapbox_access_token'];
 
     const mapStyleStr = preview ?
-        styleSpec.format(stripAccessTokens(style.replaceAccessToken(this.props.mapStyle))) :
+        styleSpec.format(stripAccessTokens(style.replaceAccessTokens(this.props.mapStyle))) :
         styleSpec.format(stripAccessTokens(this.props.mapStyle));
     const styleTitle = this.props.mapStyle.name || 'Style';
     const htmlStr = `

src/components/modals/SourcesModal.jsx

@@ -236,9 +236,12 @@ class SourcesModal extends React.Component {
         <p>
           Add one of the publicly available sources to your style.
         </p>
-        <div style={{maxwidth: 500}}>
+        <div className="maputnik-public-sources" style={{maxwidth: 500}}>
         {tilesetOptions}
         </div>
+        <p>
+          <strong>Note:</strong> Some of the tilesets are not optimised for online use, and as a result the file sizes of the tiles can be quite large (heavy) for online vector rendering. Please review any tilesets before use.
+        </p>
       </div>
 
       <div className="maputnik-modal-section">