configure: added --with-libgmx to allow to compile against double precission
configure: added --with-libgmx to allow to compile against double precission

Pallavi-Banerjee21/votca.csg,Pallavi-Banerjee21/votca.csg,vaidyanathanms/votca.csg,vaidyanathanms/votca.csg,vaidyanathanms/votca.csg,vaidyanathanms/votca.csg,Pallavi-Banerjee21/votca.csg,Pallavi-Banerjee21/votca.csg,vaidyanathanms/votca.csg,Pallavi-Banerjee21/votca.csg,Pallavi-Banerjee21/votca.csg