Main menu and packet list menu updates.

Main menu and packet list menu updates.

Enable and disable packet list-relasted menu items in one place. Add
"Colorize Conversation" items to the packet list context menu.

In the GTK+ UI we tend to disable entire menus, which makes their items
inaccessible. Try not to do that in the Qt UI so that menu items are
always visible even if they're disabled.

Remove commented items which are now complete.

Change-Id: I69b878b45334bf88014694b1bf016278fa55a94b
Reviewed-on: https://code.wireshark.org/review/9819
Reviewed-by: Gerald Combs <gerald@wireshark.org>