Add support for building MSI and EXE installers with WiX.

Task-number: QBS-16

Change-Id: I16a520863991a5d85ed7cb753ce3d95fb33b5c01
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>