Add hash2kmer.py code to get potential genes and sequences for each k-mer hash

[olgabot]

Is your feature request related to a problem? Please describe

Currently, there is no automated way to go back to the sequence creating the hash for each k-mer. There is code to do this, like here but it is not yet integrated into kmermaid. Since there are often questions about what k-mers contribute to the cell type, having the underlying sequence and read associated with each k-mer would be very useful.

Describe the solution you'd like

Add hash2kmer as a process, performing it on each cell's signatures individually. For bam input, keep aligned and unaligned separate.

Describe alternatives you've considered

The way I do this right now is in a hacky Jupyter notebook.