added if(iextZero) to saver time in assemble

cardmech/conf/cellmodels.conf

cardmech/conf/elphy.conf

cardmech/conf/m++.conf

cardmech/src/CMakeLists.txt

cardmech/src/ExternalCurrent.cpp

cardmech/src/ExternalCurrent.hpp

cardmech/src/cellmodels/MBeelerReuter.cpp

cardmech/src/cellmodels/MCellModel.cpp

cardmech/src/cellmodels/MCellModel.hpp

cardmech/src/electrophysiology/MainMonodomain.cpp

cardmech/src/electrophysiology/assemble/IElphyAssemble.cpp

cardmech/src/electrophysiology/assemble/IElphyAssemble.hpp

cardmech/src/electrophysiology/assemble/Monodomain.cpp

...ch/src/electrophysiology/assemble/MonodomainSplitting.cpp

cardmech/src/electrophysiology/solvers/SplittingSolver.hpp

cardmech/test/electrophysiology/TestMonodomain.cpp