Make mobile data indicator more robust
Currently phosh displays an orange exclamation mark around the cellular signal strength indicator when cellular data is disconnected. It could still be improved in a few ways:
- differentiate between "data enabled, but unavailable" and "data disabled by the user" states. Only the former is an error state, the later is the expected state and shouldn't cause visual warnings (it could still be indicated with some icon, but orange exclamation mark isn't appropriate there)
- display the exclamation mark (or a different icon) also when the connection is in progress - currently it's only displayed after the connection fails, but not when it's still connecting, which gets confusing when it takes a long time for connection attempt to time out