Login error handling message for invalid username

Username error message shows which user accounts are configured.
Attacker can guess the username. Message should be more generic so that
an attacker cannot guess a configured user account.
Login error handling message for invalid username

non-english lexicons
Login error handling message for invalid username

* origin/pr/11165:
  Login error handling message for invalid username
  Login error handling message for invalid username

Conflicts:
	core/lexicon/es/login.inc.php
	core/lexicon/et/login.inc.php
	core/lexicon/fr/login.inc.php
	core/lexicon/it/login.inc.php
	core/lexicon/nl/login.inc.php
	core/lexicon/pt-br/login.inc.php
	core/lexicon/sv/login.inc.php
	core/lexicon/th/login.inc.php