Implementation of Track loading

Use leaflet-filelayer to load kml, gpx, geojson, json tracks and display them as new Overlay layer.

js/plugin/TracksLoader.js

@@ -0,0 +1,63 @@
+BR.tracksLoader = function(map, layersControl) {
+    TracksLoader = L.Control.FileLayerLoad.extend({
+        options: {
+            layer: L.geoJson,
+            layerOptions: {style: {color:'blue'}},
+            addToMap: false,
+            // File size limit in kb (default: 1024) ?
+            fileSizeLimit: 1024,
+        },
+
+        _initContainer: function () {
+            var thisLoader = this.loader;
+    
+            var fileInput;
+            var container = L.DomUtil.get('navbarLoadTracksContainer');
+    
+            // Create an invisible file input
+            fileInput = L.DomUtil.create('input', 'hidden', container);
+            fileInput.type = 'file';
+            fileInput.multiple = 'multiple';
+            if (!this.options.formats) {
+                fileInput.accept = '.gpx,.kml,.json,.geojson';
+            } else {
+                fileInput.accept = this.options.formats.join(',');
+            }
+            fileInput.style.display = 'none';
+            // Load on file change
+            fileInput.addEventListener('change', function () {
+                thisLoader.loadMultiple(this.files);
+                // reset so that the user can upload the same file again if they want to
+                this.value = '';
+            }, false);
+    
+            var link = L.DomUtil.get('navbarLoadTracks');
+            L.DomEvent.disableClickPropagation(link);
+            L.DomEvent.on(link, 'click', function (e) {
+                fileInput.click();
+                e.preventDefault();
+            });
+            // dummy, no own representation, triggered in loading menu
+            return L.DomUtil.create('div');
+        }
+    });
+    var tracksLoaderControl = new TracksLoader();
+    tracksLoaderControl.addTo(map);
+
+    tracksLoaderControl.loader.on('data:loaded', function (event) {
+        var layer = event.layer;
+        layersControl.addOverlay(layer, event.filename);
+        layer.addTo(map);
+    });
+
+    tracksLoaderControl.loader.on('data:error', function (event) {
+        var err = event.error;
+        BR.message.showError(
+            i18next.t('warning.tracks-load-error', {
+                error: err && err.message ? err.message : err
+            })
+        );
+    });
+
+    return tracksLoaderControl;
+};