Update sctransform recipe

[Sichao25]

• Modified sctransform function and recipe. Now sctransform will only be performed on adata.X. Other layers will get normalized by size factors by default.
• Users can run the sctransform on all layers manually, this will raise a warning.

[Xiaojieqiu]

thanks Sichao! this is great. Have you also implement the same procedure for pearson residual?

[Sichao25]

thanks Sichao! this is great. Have you also implement the same procedure for pearson residual?

Modification on person residuals is in another pull request. Also, the monocle_perason_residuals recipe has already implemented the correct way to perform the preprocessing.