Wraps all access to the account in a transaction so any updates
done to the account must be done in the same transaction, making the
update atomic between tabs.

Doesn't do any migration from localstorage yet.

Rather than a promise which relies on the caller's promise handler
code being run in the same tick which is not guaranteed.

To avoid throwing away all the data for anyone running firefox in
one of the modes where indexedDB is broken.

This was entirely unnecessary and hopefully make things a bit
simpler to understand and has fewer asyncs flying around.