Make Qt relocatable and add a script for auto-fetching the prebuilt deps from the CI builds

To fetch the deps you'll have to type:

mkdir b
cd b
cmake -G "MinGW Makefiles" -DCMAKE_INSTALL_PREFIX=..\i ..\krita\build-tools\ci-deps\
cmake --build .

And you should have the all the deps installed! :)

PS: Until the patch is merged the deps built on the CI are not relocatable. So the script will let you build Krita fine, but it will refuse to start. CI deps should be rebuilt first.