Fix gmail auth dialog popping up over and over again.
Summary:
This happened when entering "david.faure" as username in the
account dialog, without "@gmail.com".
Normalize gmail username so that it matches the JSON account info
returned by GMail authentication.
Test Plan:
Entering david.faure as username and saving,
leads to gmail.com appended (both in the auth dialog and when reopening
the account configuration dialog).
Reviewers: dvratil
Reviewed By: dvratil
Subscribers: kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D14852