Updates
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* better defaults for `filter_and_normalize()`
* add an `ignore_ig` option to `dimensionality_reduction()` which ignores immunoglobulin genes during PCA, clustering and UMAP embedding
* added `bar()`, `scatter()` and `umap()` functions to `scab.pl`
* default `obs` field for assignments when using `demultiplex()` was changed to `cellhash_assignment`
* add a `concat()` method to `scab.io` which concatenates multiple `AnnData` objects
* general bugfixes