Fix file output for cell model history point filter

Issue/feature addressed

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.

Proposed solution

Update the CellModelHistoryPoint filter to have its own code for writing out to file.

Implementation

The 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.

Tests

Notes

None

Checklist

• Functions and classes, or changes to them, are documented.
• User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Newly added files are correctly formatted.
• License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).