When the GET request from askFromUser is scheduled on the QNAM inside
the slot that handles the QNetworkReply::finished signal, it seems to
not get processed at all.
This workaround moves the sending of the new GET to the event loop,
sidestepping the problem.
The re-enables the UI, uses Qt API for importing and
stores the certificate/key in the system keychain.
People who had set up client certs need to re-setup the account. This is ok
since it was an undocumented feature anyway.
This moves the responsibility of asking the user or not for
credentials from the Credentials classes back to the AccountState.
fetch() now only extract credentials from the keychain, reports
the result to the AccountState which then decides if askFromUser()
should be called or not. The result is once more reported to the
AccounState.
This also replaces the HttpCredentials::queryPassword virtual
which now lets HttpCredentialsGui and HttpCredentialsText do it
the way that they prefer.
