Refactor focuslock-public, implement getter methode

[derpixler]

Now you can use the Methode get_focuslock_image( 99 )

Example:

args = [
    'id'        => $attachment[0],
    'size'      => 'large',
    'classes'   => 'gal'
];

$attachment = get_focuslock_image( $args );