Update Z index for iony admin panels so they are on top

Set all Ionyweb z-index values above 9000 so the admin
always displays above the theme if the user follows the
defined standard of not using any index above 9000.
Documents z-index standard for Ionyweb admin panels

Adds documentation warning the user not to set the
value of z-index above 9000 so as not to conflict
with Ionyweb