Fixes for SC.TemplatePoo to help it work with updated SC.CoreView.
Fixes broken unit tests.
Updates replaceLayer to reattach when previously attached.  Also watches out for automatic attachment on creation that is done by childViews.
Fixes a problem with SC.ImageView and static layout that was hacked around and fixes a bug where starting with no value and then adding a CSS sprite value.
Moves the layout code into SC.View's layout module, also fixes notification code arround attaching & detaching.
Fixes SC.ControlTestPane cleanup to destroy the pane.
Improves do show and attached handling to properly update child views.
Bumps the Showcase submodule.
Notifies after updating visibility so that willShowInDocument can measure the element if necessary.
Improves setStyle in SC.RenderContext to not remove all styles in order to set the updated hash.
Tidies a bit.