Switch to customized leaflet-sidebar-v2 (WIP)

Based on leaflet-sidebar-v2 fork of sidebar-v2:
- Simpler because Leaflet-only
- autopan option
- seems more active with two contributers

Customization for brouter-web in own fork (WIP):
- hidden bar when collapsed
- flat design to match header/footer
- flexbox layout beside map instead of media breakpoints

js/index.js

@@ -219,7 +219,7 @@
 
         trackMessages.onAdd(map);
 
-        sidebar = BR.sidebar('sidebar', {
+        sidebar = BR.sidebar({
             listeningTabs: {
                 'tab_data': trackMessages
             }