Add rudimentary location support

This is an untested proof-of-concept for how #59 could get handled. I didn't dig too much into how the server is actually wired up to the `UBWindow`, so there could be an issue with this particular approach where the widgets are loading before the location data is injected to the webview's `window`.

It also probably makes more sense to have the location delegate use `callWebScriptMethod:withArguments:` when the location changes, so the script could actually respond to the changes. This probably just needs to call `refresh`, or there could be a more explicit function that gets called. 

Happy to spend more time on this if it's something you think would make it in.