Enable installation of ResInsight with a package manager through an option

This patch is an attempt to find a compromise between the needs of building ResInsight in an enterprise setting where binaries are delivered to a specific directory, and as part of a regular distro packaging where binaries should end up at pre-determined locations.

By *default*, the install target works as before: All final deliverables are put in Install/ResInsight-0.9.0. This also includes a local copy of the Qt libraries. The executable is coded to load libraries from its own directory.

If the option -DPRIVATE_INSTALL=OFF is given to CMake, the build produces an `install' target which copies files to LSB-compilant locations. No libraries are bundled.