Better support for offline / low connectivity

During the first time flow, if users can't connect to a network, they get an infinite spinner that blocks them from further action.

We should allow users to do as much as possible without any network connection, while continuously attempting to connect in the background.

Once connection is absolutely necessary, and if Metamask is still attempting to connect, we should give the user an action to take (even if that is just 'please wait')

Alongside this we should investigate to see if there are any bugs that are causing more network loading spinners than necessary.