ApplicationPage: Fix gap under carousel caused by invisible InlineMessages

This required some trickstery, but there you have it for not managing InlineMessage's padding internally. The biggest issue here, of course it the inability of Repeater to provide a declarative API to track all of its delegates in one expression; and the uselessness of its visibleChildren property, since Loaders can't set them to be invisible, because implicit propagation of visibility would break core logic of InlineMessage component.