Dckit

- enh: allow keyword argument --version (print version and exit)
- build: pin PyQt5 to 5.14.2 on Linux/macOS
- build: macOS build was not working

- fix: export file names were allowed to have invalid characters
- fix: ignore ResourceWarning
- enh: improved preview speed for .tdms data
- setup: bump dclab from 0.25.0 to 0.27.5 (support ML features)
- setup: bump imageio to >=2.8.0
- setup: bump nptdms to >=0.27.0
- setup: drop shapeout dependency

- fix: display success dialog after joining datasets

- setup: bump dclab from 0.22.7 to 0.25.0 (fixed broken "index"
feature when joining datasets, improved HDF5 writer and
dataset checker)
- setup: bump shapeout to 1.0.9 (possible issues with file system
crawler)

- enh: show dataset values when metadata are wrong (dataset checker)
- enh: improve layout spacing for dataset checker
- setup: bump dclab from 0.21.2 to 0.22.7 (compression info,
autocheck of metadata, flow rate check, export fix)
- docs: to avoid confusion, be more verbose when the user clicked
"Update metadata" and there is nothing to do (7)
- ref: revert "fix" from 0.8.1

- fix: HDF5 files were not always closed properly when writing logs
(reverted in 0.8.2, because essentially just refactoring)