Myokit

- Bugfix in PyQt4 support.

- Fixed PyQt4/5 and PySide compatibility issue that was causing errors in the DataBlock viewer's open function.

- Added missing pragma directive to enable double-precision simulations OpenCL.

- Added support for PyQt5.

- The IDE now has a model navigator, that displays the model components alphabetically and lets you navigate large models more easily.
- Fixed a bug in the implementation of `DataBlock1d.grid()`, and updated its documentation: this method returns coordinates for squares where each square represents a data point.
See the [Stewart 2009 OpenCL example](http://myokit.org/examples/#stewart-2009) for an example of its use.
- Added a second method `DataBlock1d.image_grid()` that returns coordinates for points where each point in space represents a data point.
- Fixed bug with Ctrl+Shift+Home in IDE.
- Various small bugfixes in IDE.
- Updated installation instructions on website.

- Fixed bug (with new numpy) in `DataLog.split_periodic`.
- Fixed warnings in GDE.
- Fixed issue with pyside/pyqt difference.