Eliminates the need to call layout() explicitly on *LayoutPanel, which
should greatly simplify their use. RequiresLayout becomes
AnimatedLayout, which is now just a convenient moniker for the ability
of a panel to layout its children.

This also necessitated a change to LayoutPanel, such that it no longer
exposes the underlying Layout.Layer objects associated with each widget.

Review: http://gwt-code-reviews.appspot.com/89818

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@6624 8db76d5a-ed1c-0410-87a9-c151d255dfc7
19 files changed