Version cleanup

[bscrow]

1. Clean up versioning so the package works across mainstream Python and package versions.
2. Update conda.yaml with package requirements, and add conda-scimap.yaml, which builds an environment with stricter version constraints so that SpatialCells and scimap can run together.
3. Make minor updates to the tutorial notebooks to account for method-calling changes in newer versions of seaborn and anndata.
4. Carry over critical bug fixes with cleaner comments. Supersedes Bugfix/V1.0.1 #25.