This introduces three network states:
1. completely disconnected
2. connected only via metered networks
3. connected via unlimited networks
This allows the update process to use bandwidth better, especially when the
user has enabled the "Only on WiFi" setting. It also helps prevent silly,
cryptic error messages in the update process is triggered when there isn't
internet available.
I tested this with:
* 4G only, but not set up for internet
* 4G only, with internet
* 4G + WiFi
* WiFi only airplane mode
* no internet at all, full airplane mode
closes#793closes#774
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