UI tasks to get closer to feature complete

[davecraig]

• Add FeatureTree of Markers to aid some of the following. Use a flow of MarkerData to refresh a FeatureTree? This has uses in callouts as well as in the UI
• Implement Places Nearby (there's an initial version, but it needs filtering and more UI work)
• Implement Nearby Markers
• Show Places Nearby in list for Add Waypoints. In iOS selecting a POI turns it into a Marker
• Disallow markers being created where there's already a marker (it may be that iOS has a certain radius for this?).
• Fix Location Details so that if Save Marker is picked then when it returns to the screen it shows Edit Marker immediately
• Current audio beacon is no longer appearing on map UI
• Can't select a new location with long touch from within Current Location map UI
• Fix JSON import from iOS route export so that it goes via the edit/add route page. Currently it sends to blow away all previous markers and routes...
• Add markers for route to maps
• Add "Route playing" map to home page with buttons to skip between waypoints and mute beacons.
• Add "Stop Route" to RouteDetails screen if it's currently playing
• Add FullScreen option for maps. This is available in iOS for all maps e.g. the playing route, from LocationDetails, Markers and Routes etc.