Assume no overlaps when using cell types mode for drastically improve…

[ykevu]

…d speed

• Assume that we are using data with no overlaps when in the cell types tab so that canvas responsiveness is much faster. This does mean that overlaps will cause potentially breaking visual issues if you want to do cell type labeling
• Additionally, the labeledCanvas will be set transparent when doing cell type edits, since it doesn't make too much sense to use it when doing cell type labeling
• Finally, note that the original cellTypeCanvas that supports overlaps is still in the code base, just not used until a better optimization solution can be reached
• The cell type hover UI is also disabled for now, since it was more annoying than useful while testing due to a bug where it would persist

[ykevu]

@rossbar This should be ready to go now