Optionally enable system installation of binaries

If the option PRIVATE_INSTALL is set to OFF, LSB-compliant paths are
used for the `install' target. Path to Octave plugins is taken from
the configuration program.

Default is still to install in a private sub-directory of the build.
However, the binaries get hard-coded an RPATH to load the bundled
binaries from the same directory as the program. As a consequence,
the wrapper is no longer necessary, but is provided for backward
compatibility.
Put launcher for ResInsight in desktop environment