Walking travel mode fixed

Setting the travel mode to UICGTravelModeWalking was causing the following error to be thrown

> Error Domain=org.brautaset.JSON.ErrorDomain Code=3 \"Unrecognised leading character (41)\

The bug was caused by a wrong use of *GDirections*. As stated in the google maps API documentation

> The mode of travel, such as driving (default) or walking. Note that if you specify walking directions, you will need to specify a panel to hold a warning notice to users.

then 

```javascript
gdir = new GDirections(null, null);
```
has been replaced with this

```javascript
gdir = new GDirections(null, "body");
```