Implement multiple inheritance in Help, allowing variables, fields and related

topics to be inherited from multiple entries.  Operation/Help now also gives
the help hash a default ISA array, to make downstream processing by tests and
documentation compilers easier.
Convert existing Help entries that already used ISA to have an array ref
instead of a singular hash ref.  Also update the Help skeleton to show
the new syntax.

lib/WebGUI/Help/Asset.pm

@@ -105,6 +105,11 @@ our $HELP = {
 	'asset template' => {
 		title => 'asset template title',
 		body => 'asset template body',
+		variables => [
+			{
+				name => 'controls',
+			}, 
+		],
 		fields => [
 		],
 		related => [