Added option to run configure with a parameter file.

params.conf holds all the variable definitions which are usually defined in configure.sh itself. When 'params.conf' is given as an argument to configure.sh, it now extracts all the installation variables from the file. Benefits: Create your own (personal) configure file to keep all values across different FairSoft versions; run configure.sh in a more 'scripted' way, e.g. for your experiment's default setup.

Example params.conf given, but not necessarily needed in FairSoft repo.