QtIFW

allow installing compressed packages

This change introduces new feature to add 7z packages to be
installed. Packages must be installer repositories (created with repogen),
compressed to 7z file and named as qtbsp or 7z. Selecting compressed package
is done either with button in component selection page or with
--installCompressedRepository parameter given to installer or to maintenancetool.
Button will not be created by default. If you want to show the button
either build IFW with DEFINES+=INSTALLCOMPRESSED or enable the button in control
script with allowCompressedRepositoryInstall() in ComponentSelectionPageCallback

Task-number: QTIFW-886
Change-Id: Ia060092c348991d5195393b7dc154205f8bf92a5
Reviewed-by: Iikka Eklund <iikka.eklund@qt.io>