[map] Fix differential data support

 map.js

@@ -268,12 +268,6 @@
            }),
            text: new ol.style.Text({
                font: 'bold 10px sans-serif',
                // TODO: special directions
                // vehicle.line = vehicle.name.substr(0, vehicle_name_space);
                // vehicle.direction = normalizeName(vehicle.name.substr(vehicle_name_space+1));
                // if(special_directions[vehicle.direction]) {
                //     vehicle.line = special_directions[vehicle.direction];
                // }
                text: feature.get('line'),
                fill: new ol.style.Fill({color: 'white'}),
            }),
@@ -386,12 +380,15 @@
            api_url + '/positions/?type=' + this.prefix + '&last=' + this.lastUpdate
        ).done(function(data) {
            try {
                if(data['date'] < self.lastUpdate) {
                    console.log('Data older than lastUpdate!');
                }
                if(data['type'] == 'full') {
                    self.loadFullData(data['pos']);
                } else {
                    self.loadDiffData(data['pos']);
                }
                self.lastUpdate = data['last'];
                self.lastUpdate = data['date'];
                setTimeout(self.fetchXhr.bind(self), api_refresh);
            } catch(e) {
                console.log(e);