Reduce minimum API level more

[wvengen]

After 4e4a90b our minimum API level is 26, but we'd still like to reduce it a bit more, to support more devices.
Currently the WebView is blocking this. Perhaps WebViewCompat could help here?

[wvengen]

After 13287a6 (small WebView usage change) and f981c5b (network availability handling) we're down to API level 21, which may be fine.