add support for tweaking software version and toolkit from EasyBuild command...

add support for tweaking software version and toolkit from EasyBuild command line, i.e. override whatever is specified in the easyconfig file(s) provided;
along the way, also clean up unused imports, shorten lines that are too long, fix a bug in WRF (self.wrfsubdir being empty in make_module_req_guess), and add extra functions in EasyConfig class required to support the tweaking feature