[TASK] EXT: t3skin - Login template & JS

Moves login template and JavaScript files to directory
structure following the Flow convention.

Change-Id: Ibc8abcdb31d6de46cf544d4ddf36e299f4fe016d
Resolves: #48001
Releases: 6.2
Reviewed-on: https://review.typo3.org/20568
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer