When discovery fails to be seeded with bootstrap/fallback nodes, it
never recovers.
This commit changes the behavior so that status-go retries fetching
bootnodes, and restarts discovery when that happens.
If a contact update or a legacy contact request is sent, we create a
notification for the user in the activity center so it can be replied
to.
If at a later date a new contact request is received from the same user,
this will replace it, so the proper message can be displayed.
Andrea Maria Piana
Richard Ramos