New Functionality: Emmbed new cells

Embed new cells in an already existing space

You can now use an existing embedding to add new cells via embedNewCells. Briefly new cells are first normalized with GF-ICF method but using as ICF weigth estimated on the training set and than projected in the existing PCA/LSA space before to be embedded in the already existing UMAP space via uwot::umap_transform. See the example here about this new functionality.