Add option to use anndataR to read in tables

[LouiseDck]

Current usage:
Install anndataR as such:
devtools::install_github("keller-mark/anndataR", ref = "spatialdata")

Changes:

in file read.R

• add readTable_anndataR function that uses anndataR to read & convert to SingleCellExperiment
• rename readTable to readTable_basilisk
• add readTable function that disambiguates between the two functions based on a parameter passed by readSpatialData

in file test_methods.R

• add test that reads using anndata & basilisk & zellkonverter and one that uses anndataR, check for differences

[LouiseDck]

I think this should probably only be merged here when this PR in anndataR is merged.