QtIFW

Add possibility to specify a control script.

Right now we support control scripts just as command line argument,
but now we can also bundle it in the binary as well. This helps e.g.
with running scripts during uninstallation, enables the possibility
to modify the introduction page or enables headless installer builds.

Task-number: QTIFW-495
Task-number: QTIFW-166
Change-Id: I6fee6a55db78ed28b1eeb8257a4febaa2703c04e
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>