connection state design

we currently have several icons

• wwan signal strength
• wwan network type
• wifi state (connection to ap and strength in one icon)
• soon bluetooth (#220 (closed))
• soon wired connections ('desktop' use case) (#259)

but there's no 'can reach the internet' indication. @julian.sparber folded that into !401 (closed) which is think is not ideal since all of the connection types need this property, not only wifi:

• wwan can have a signal but no data connection enabled
• wifi can associate to an ap but needs a captive portal
• bluettooth network can (but usually doesn't) provide ip access
• wired connection can get an ip but be stuck behind a corporate firewall

(on top of all that is VPN tunnels)

so either each of these methods needs to indicate 'internet reachability' or we need a single indicator. I'd be good to have a design discussion here.

/cc @francois.techene @tobias.bernard @sam.hewitt