Myokit

- Various small bugfixes.

- Updated step method to accept models as reference.
- Reinstated `Model.load_state()` method.
- Imrpoved find dialog.
- Various small bugfixes.

- Added quick var info to gui.
- Renamed `current_diff` to `diffusion_current`.

- Added on ChanneML import.
- FiberTissueSimulation now works with 2D fibers.

- Added data extraction features to abf format.
- Added on Fiber-Tissue simulation class.
- Various improvements and bugfixes.

- Number of cells to pace can now be set in `OpenCLCableSimulation`.
- Added function to find origin of NaN errors in an `OpenCLCableSimulation`.
- Updated SimulationLog to return mesh grid for pyplot.
- Added 1D CV calculation to `SimulationLog`.
- Renamed cable simulation classes.
- Made 1D OpenCL Simulation suitable for 2D use.
- Added method to list component cycles.
- Added a method that checks which variables cause mutually dependent components.
- Various small bugfixes.