Dcnum

- fix: there was no progress for background copying
- enh: detect data files that contain no events
- tests: add test for sparsemed bg worker
- tests: add test for logic json encoder

- enh: define valid DCNumJobRunner state
- enh: more robust computation of progress
- enh: use HDF5Data when loading input data for background computation
- enh: automatically split segmenters and extractors equally
- ref: reduce default image cache size from 5 to 2
- ref: move dataset generation default kwargs to writer submodule
- ref: warn above 0.5% of discarded events in EventExtractorManagerThread

- fix: ignore empty HDF5 datasets when copying metadata
- fix: logging from subprocesses did not work as expected
- enh: warn user about total number of invalid masks
- enh: introduce DCNumJobRunner.error_tb for errors happening in threads
- enh: improve logging verbosity
- enh: append job information as log entry in DCNumJobRunner output file
- enh: set chunk size for all feature data to 1MiB in HDF5Writer
- ref: removed close_queues argument from EventExtractor init
- ref: rename event_count with image_count in background computation
- ref: do not print anything to stdout when computing background data
- ref: use data from background computer in DCNumJobRunner.get_status

- fix: when checking for ppid kwargs, allow kwargs defined in `__init__`
- ref: use kwonly arguments for segmenter `__init__` method
- tests: set environment variables so that libraries use one thread only

- feat: implement "copy" background class
- fix: handle small kernel size before background computation (16)
- fix: update experiment:run identifier for dclab-user convenience
- fix: make sure output directory exists for pipeline job
- fix: forward debugging flag to SegmenterManagerThread
- ref: reduced minimum frame count for rolling median background
computation to kernel size

- BREAKING CHANGE: Remove preselection capabilities, because it is not
well integrated into the pipeline. For more information, please see
issue 15.
- feat: introduce logic submodule for running pipelines
- feat: implement HDF5Writer.store_log
- enh: add Segmenter.hardware_processor property
- enh: introduce pipeline identifier for data pixel size
- enh: reduce pixel_size accuracy to 8 digits after the decimal point
for pipeline reproducibility
- enh: warn the user when creating a basin-based file without basin paths
- ref: deprecate pixel size correction in HDF5Data
- ref: increment DCNUM_PPID_GENERATION to 7
- ref: several changes and deprecations in the PPID helper functions
- build: change flat-layout to src-layout (issues with editable installs)