Save own device verification quickly for 4S key share requests that follow

[jryans]

At the moment, when we save own device verification locally, there are various async steps in the way, so we don't set our local trust of new device right away.

This causes problems when the other device then sends a key share request, because we only approve those for trusted devices.

We should either streamline the code so that device trust is saved locally immediately, or use a different mechanism to track devices we have just trusted for the purpose of approving 4S key shares.