localizable menus. Refs: #80.
Mostly as proposed by Helmut Zinn and Ivan Denisov in CPC 1.7 rc5.
Menu items with a TAB inside are now supported by Dialog.MapString.
Key 'PageSetup' reused instead of introducing a new key 'Page Setup' in System/Rsrc/Strings.
Key 'HelpContents' renamed to 'Help Contents'.

Signed-off-by: Josef Templ <josef.templ@gmail.com>