Myokit

- Added IV curve experiment.
- Improved error detection in CVODE simulation.

- Added a diffusion on/off switch to the OpenCL simulation.
- The OpenCL sim can now replace constants by scalar fields.
This allows it to be used to test parameter influence or to simulate heterogeneity.

- Better handling of unknown units.
- Added `eval_state_derivs` option to GUI.
- Added trim trailing whitespace method to gui.
- Gui and step script now show numerical errors if they occur.
- Added `trim()` and `itrim()` methods to simulation log.
- Added a 2-variable parameter range exploration class.
- DataBlock viewer now can export frames and graphs.
- Various improvements and bugfixes.

- Added method `Model.set_name()`.
- Updated installer script for GNOME/KDE.
- Various small bugfixes.

- Added on Strength-Duration experiment.
- Added method to create cumulative current/charge plots.

- Changed `SimulationLog.integrate()` to use left-point rule instead of midpoint rule.
This makes much more sense for the stimulus current when using CVODE.
- Various improvements and bugfixes.