In the CardiacEPSolver, the CellModelHistoryPoint filter did not correctly write out data to file. This was because of changes which had been implemented in the base class HistoryPoint filter.
Update the CellModelHistoryPoint filter to have its own code for writing out to file.
v_WriteData function was overridden in the class to provide a working implementation and called from the
v_Update function when data needs to be written to file.