New app: Firefox Klar

This is a version of Firefox Focus without dependency on GMS and with telemetry off by default (can be enabled in preferences).

Closes rfp#235 (closed).

I'm not quite sure whether we should change the name and package ID. Currently we don't patch the code, but Mozilla's track record suggests that we may need to make modifications one day. Maybe it's not worth adding the app at all because maintenance cost is unpredictable.