Instead add it as a configurable path with the one from
the source directory as the default.
Also reinstates that settings/defaults.php is installed as
settings/settings.php.
Just make cmake install a small stub that includes
the settings from the build directory and then the
script from the source directory. Remove executable
rights from php files in utils/ so that they cannot
be accidentally executed.
Executables (including websites) need to be installed in the
build directory, so that they can find the right settings.php.
settings now defines build and source dir.