Improve the way that the NSIS installation is found.

Now that we have registry access, we search the registry for the known
key and then determine the NSIS installation path and version number
from that. The latter is now available as a set of properties.

This searching code is also now not broken for 32-bit Windows...

Task-number: QBS-414
Change-Id: I93a0e35084d11b3b0664bfa67bea29eb72a96380
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Centralize architecture canonicalization data.

Task-number: QBS-403
Change-Id: I814cdc93adafdcdbc66ec6b72fc9e98c6a7b866d
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>