Windows: Add Support for Windows SDKs

Detect SDKs before VC installations. Add static list of installations
initialized on demand. List SDKs and VC with platforms settings
depending on Qt-version. Detect installations properly, checking
existence of setup scripts. Handle delayed shell variable expansion used
by SDK setup scripts. Tested with SDK 6.1 onwards (32bit/64bit).
Reviewed-by: Daniel Molkentin <daniel.molkentin@nokia.com>