Harmonize WinRT documentation with other platforms

The order or documentation is now more consistent with iOS and Android.
Also added some further clarifications about requirements on the
development host.

Added Windows Runtime to the Getting Started List.

Change-Id: I8a8b85f7a268184ec046f2a69c3b90dbe0d05549
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>