Implement a file layer for gpx,kml,wkt support.

src/Bundle/Resources/config/layers.yml

@@ -45,6 +45,10 @@ parameters:
         extend: true
         fit:    true
 
+    file:
+      children: false
+      icon: 'bundles/netzmachtcontaoleaflet/img/file.png'
+
 services:
   _defaults:
     public: false

src/Bundle/Resources/config/mappers.yml

@@ -58,6 +58,10 @@ services:
     tags:
       - { name: netzmacht.contao_leflet_maps.mapper }
 
+  netzmacht.contao_leaflet.mapper.file_layer:
+    class: Netzmacht\Contao\Leaflet\Mapper\Layer\FileLayerMapper
+    tags:
+      - { name: netzmacht.contao_leaflet.mapper }
 
   # Control mappers
   netzmacht.contao_leaflet.mapper.zoom_control: