[Lazarus] New menu designer

[Juha Manninen]

Hello

I committed a new Menu Designer by Howard Page-Clark in r50992.
See:
  http://bugs.freepascal.org/view.php?id=29205

Please test.
It has some interesting design decisions. I initially see some things
that may need fixing:

1. The main menu top level items do not show any indication when
selected. They need some indication although it can be different from
the other menu items.

2. A popup menu for a menu item has "Create OnClick handler" and "Edit
Caption" entries side by side with the Add... and Move... items. They
don't make a good match. Those entries duplicate the OI functionality
and could be removed, or maybe moved to another section in the popup
menu.

3. "Checkmark and radioitem properties" dialog should be removed. It
is a modal dialog and always goes behind the menu designer. The menu
designer itself tries to stay on top.
The checkboxes can be moved to a popup menu section as checkable menu items.
They also duplicate OI functionality and are not really necessary.
The GroupIndex feature does not work. It can be moved to the menu
designer main window (and fixed).

I tested on Linux with GTK2 and QT.
Trunk is open for new features and improvements after 1.6 was branched.
Opinions of this menu designer please.

Regards,
Juha