Create a GeoClue2 "Agent" [$100]

Apps should have to present a request to the user before being allowed to access location data. Luckily, GeoClue2 already implements this as part of the library, we just need to implement the UI for (aka the Agent).

See the API documentation here:

A design for this needs to be:

* A dialog
* With actions that indicate granting permission or denying permission
* With the default action (keyboard focus) of Deny
* Presenting the application name (and maybe icon) asking for permission
* Presenting the service we're asking permissions for (location)
* Presenting the accuracy level of information requested (country, city, neighborhood, street, exact)