Export path to the installer binary to the component script

Qt framework has LGPL license that allows using the libraries
in closed-source projects as shared libraries.

I didn't find what license is acceptable for Qt Installer Framework, so
I guess it's the same as Qt's license.

So I suppose one may not use the framework for closed-source installer.

Also closed-source projects must build Qt as dynamic library and
therefore developers need to compile two builds of Qt: first (dynamic)
for a project and a second (static) for an installer.

One way to workaround this is to build the installer framework against
dynamic Qt library but in this case there are many files instead of one
executable installer. Developer may package all these files to
a self-extracting archive that after extraction runs the installer.

The last issue in this scheme is that shared Qt libraries must be copied
to a destination path of an application. To do so one should know
a path to an installer's executable.

I didn't find a way to get the path to an installer (I mean getting
a path in script files via exported variables) so I suggest to add
this possibility to the Qt Installer Framework.

component.addOperation("Copy", "@InstallerPath@/libQtCore.dll", "@TargetDir@/");

A patch with probably changes is attached.