Improved Support for Runtime LAF Switching

This patch fixes the majority of issues when switching from WebLAF to another LAF at runtime.  There are still a couple of minor issues I haven't figured out yet, but this patch fixes the majority of things.

What's included:

   * Fixed bug - keep user borders if they're instances of UIResource,
     not BorderUIResource
   * In UI delegate classes, set opaque property with LookAndFeel.installProperty()
     to avoid overriding possible values set by the developer.
   * Don't call setOpaque(true) in UI delegate uninstall() methods; standard
     LAFs don't do this either.  Can cause issues.
   * WebButtonUI should remember previous values of several button properties
     so it can revert them back to the previous values.
   * WebListUI should set colors wrapped in ColorUIResources.
   * Label foreground and disabled foreground set in UIDefaults table for
     convenience.
   * Removed unnecessary code in WebTextPaneUI.
   * WeblafBorder now extends EmptyBorderUIResource.
   * Table.scrollPaneBorder set to null in UIDefaults to avoid it becoming
     a bevel border due to the changes above.
   * Remove custom minimize/maximize buttons when uninstalling WebRootPaneUI

BTW - this LAF is super easy to configure and use, good job!  Much cleaner than Substance.