Dclab

- fix: do not cache hierarchy child feature values; this might lead
to intransparent situations where a child has different features
than its parent (you cannot always rely on the user to call
`apply_filter`)
- fix: hierarchy child configuration section "calculation" was not
updated with the hierarchy parent values
- docs: add example for loading data from DCOR and computing
the Young's modulus

- fix: support unicode characters when writing HDF5 in Python2

- docs: add artwork
- fix: support unicode characters in sample names in Python2

- docs: add more information on emodulus computation
- docs: add script for visualizing emodulus LUTs

- ref: replace deprecated .tostring() with .tobytes()

- fix: video seek issue workaround also for the first 100 frames
- cli: also skip the final event in tdms2rtdc if the image is empty
- cli: renamed kwarg `--include-initial-empty-image`
to `include-empty-boundary-images`
- enh: improve detection and recovery of missing images for fmt_tdms