Detect if a device does not support Depth API

[MrCsabaToth]

It turns out that Motorola Thinkphone doesn't support the Depth API (https://developers.google.com/ar/devices#google_play_devices). The app runs but never locks in the AR scene. There should be a warning.

[MrCsabaToth]

I'm not 100% sure if Depth API is required for the Geospatial API or not.

[MrCsabaToth]

Per Dereck the Depth API should not affect this. This is probably rather #26