Sidpy

Small update to sidpy. Changes since last version:

- Added CHANNEL dimension type for sidpy dimensions (for example of usage see this [link](https://github.com/pycroscopy/pycroscopy/issues/273#issuecomment-1267480139)) . This is useful for multi-channel spectral datasets, which can now be plotted using the intrinsic .plot() method
- Added updated capability on spectral visualizer to enable plotting of multi-channel spectra
- Small changes with set_dimension() method to be more robust
- Minor bug fixes
- Updates to various tests

This release adds a few 'under the hood' changes to the sidpy dataset object, with respect to chunking and folding/unfolding. Some minor edits to some visualization functions were also made. A new method `visualize_fit_results()` to the `SidFitter` class was added to aid in visualization of functional fits.

Added fitter class and improved tests.

Minor bug fixes
Support of thumbnails for icon view of directory

updated for new version of ipyfilechooser

Update with
- better support of dask functions (thanks Mani).
- nested dictionaries are now written and read from hdf5 files
- support of 4D image sets in plotting.
- Minor bug fixes