Better decided on low/medium/high connection speed.

This adds support for navigator.connection.type to determine 2g/3g/wifi on Android devices. Fallsback to 'low' connection speed behaviour if on 2g/3g.

This should reduce the number of people getting the full bandwidth experience which appears unreasonably high currently.

@phamann @commuterjoy - You probably still want to adjust the page load timings that determine low/medium/high when this API is not supported.