Fix occasional crash from signing out in accounts view
Fixup naming of accounts manager internal property
Fixup integration with authentication updates in 2deaf64

Prevent endless loop from the authenticator
handling app-did-become-active notifications too
early. Do this by setting up a one-time
did-become-active observer in the accounts manager
constructor if the latter is called right after
app launch to only load persisted accounts after
the first did-become-active notification.
Fixup incomplete account model updates in 7fb288a

Clarify the default credential identifier.

Harden updating the credential identifier.

Properly have the account model assume
responsibility of fetching persisted credential
from a its own identifier.

Also properly allow the authenticator to
relinquish that responsibility.

Ultimately the above defects led to the accounts
manager falsely identifying new accounts as
duplicates because the same credential was being
returned, leading to the same person info, etc.
Fixup method to update persisted keychain credential

The removed call to delete any existing credential
actually prevented updating any credential. It
also somehow prevented, possibly due to a race
condition, the deletion prevents the proper
subsequent addition of the same credential. 

Ultimately, this led to a persisted account
requiring re-authentication upon being loaded from
disk the second time.
Harden accounts persistence in accounts manager

Also persist when selected account changes. This
ensures the user defaults are up-to-date. There's
not an overhead from writing to disk unless the
number of accounts changes.

Minor logging additions.
Wait for nation slug prompt alert to fully dismiss before switching to Safari
Minor whitespace