[python] Early error for dataframe objects presented as obsm etc. on ingest

[johnkerl]

The obsm, obsp, varm, and varp must be 2D arrays, not dataframes. In those cases when an input AnnData object does contain a dataframe in any of these slots, the ingest fails (as it should) but it fails partway through the ingest, and it fails with a stack trace.

• We should have a type-check early on in from_anndata (next to the other existing error checks) -- before the ingest starts -- not within the ingest-matrix function at which point the experiment-level ingest would crash partway through
• The error message should be user-friendly

[johnkerl]

@jp-dark or delegate will handle this for the upcoming sprint.