OO-4888: beautify user name panel

src/main/java/org/olat/user/ui/admin/authentication/_content/authentications.html

-<div class="form-group $f.getElementCssClass($item) o_user_edit_username clearfix">
-	$r.render("username_LABEL", $f.getItemId("username"), "col-sm-3")
-	<div class="col-sm-3 form-inline">$r.render("username") $r.render("edit")</div>
-</div>
-
-$r.render("table")
+<fieldset>
+	<legend>$r.translate("change.username.title")</legend>
+	<div class="form-group $f.getElementCssClass($item) o_user_edit_username clearfix">
+		$r.render("username_LABEL", $f.getItemId("username"), "col-sm-3")
+		<div class="col-sm-3 form-inline">$r.render("username") $r.render("edit")</div>
+	</div>
\ No newline at end of file
+</fieldset>
+<fieldset>
+	<legend>$r.translate("authentications.title")</legend>
+	$r.render("table")
+</fieldset>

src/main/java/org/olat/user/ui/admin/authentication/_i18n/LocalStrings_de.properties

 #Fri Jun 05 15:17:38 CEST 2020
+authentications.title=Authentifizierungen
 change.providers=Login
 change.providers.on=Login Name adaptieren
+change.username.title=Benutzername \u00E4ndern
 edit.title=Bearbeiten
 general.error.unique=$org.olat.user.propertyhandlers\:general.error.unique
 login=$org.olat.admin.user\:table.auth.login
 provider=$org.olat.admin.user\:table.auth.provider
+table.auth.login=Loginname
 username=$org.olat.admin.user\:form.username
\ No newline at end of file

src/main/java/org/olat/user/ui/admin/authentication/_i18n/LocalStrings_en.properties

 #Fri Jun 05 15:17:38 CEST 2020
+authentications.title=Authentications
 change.providers=Login
 change.providers.on=adapt login names
+change.username.title=Change user name
 edit.title=Edit
 general.error.unique=$org.olat.user.propertyhandlers\:general.error.unique
 login=$org.olat.admin.user\:table.auth.login
 provider=$org.olat.admin.user\:table.auth.provider
+table.auth.login=Login name
 username=$org.olat.admin.user\:form.username
\ No newline at end of file

src/main/java/org/olat/user/ui/admin/authentication/_i18n/LocalStrings_fr.properties

 #Wed Aug 12 07:19:24 CEST 2020
+authentications.title=Authentifications
 change.providers=Login
+change.username.title=Changer le nom d'utilisateur
 edit.title=\u00C9diter
+general.error.unique=$org.olat.user.propertyhandlers\:general.error.unique
 login=$org.olat.admin.user\:table.auth.login
 provider=$org.olat.admin.user\:table.auth.provider
+table.auth.login=Identifiant
 username=$org.olat.admin.user\:form.username