Doc: Various documentation improvements to the All Modules page.

-fixed missing links to Qt Windows Extras
-created links to the appropriate platforms
-replaced the \sa with the "Where to Go from Here" section
-marked-up the terms "Qt Tools" and "Qt Add-Ons" as they are official
Qt product names

Change-Id: I0c5d314e3e2bc0ecdb4800855a65014debde3183
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>