Look into adding network connection detection

[andreekeberg]

Could be really useful to have basic network connection detection, based on the Network Information API, provided we could implement a good enough fallback for other browsers, where a small sample file is downloaded file while the download speed is measured.

Seeing as the fallback would be based on a lot of guess work, a probability threshold (similar to the one used for hover capability detection) would need to be used, if it even seems stable enough to implement at all.