Myokit

- Added OpenCL device selection.
- Updated cumulative current plot method.

- Various small bugfixes and improvements.

- Add Powell's method to fit library.
- Added model statistics screen to IDE.
- Presence of `<import>` tag in CellML now causes exception instead of warning.
- Improved CellML import error messages.
- There is no longer a restriction on the type of expression used as a first argument to piecewise and if.
- Fixes to MathML parser and CellML import.
- Added option to extract colormap to DataBlock viewer.
- Added section about uninstalling on windows and slight hints about filesizes to website.
- Introduced "evaluator" class used for parallelized optimization algorithms. Rewrote PSO to use it.
- Added a genetic algorithm optimization method (does not outperform PSO).
- Added reset script to myo that removes all user settings i.e. the entire `DIR_MYOKIT`.
- Added version check to avoid Python3.
- Myokit for WinPython now has an uninstaller that shows up in "Add/Remove programs".
- Various small bugfixes and improvements.

- Added Python version check.
- Fitting library: Adding quadratic polynomial fit used to test local optima.
- Various small bugfixes.

- Improved export of units to CellML.
- `DataLogViewer` can now open CSV.
- Fixed windows newline issue when writing `\r\n`.
- Small fix to OpenCL memory management.
- OpenCL sim now also cleans when cancelled with keyboard interrupt.
- Added a `finally: sim_clean()` to all simulations.
- Various small bugfixes and improvements.

- Various bugs fixed in the IDE.