plot_genes: Plot several genes expression patterns
In strayMat/lineageDE: Differentially expressed genes in cell lineages

Tools for visualizing gene signals for sveral ranked genes and display their ranking informations.

produce one 3D plot per gene in querry. Each plot is a 3D representation (low dimensionnal provided in the object warpDEDataSet) of the dataset with cells colored by gene level expression.

plot_genes(data, ranking, genes.subset = NULL, order = "head",
  nb.show = 8, reg.f = "loess", span = 0.75, s.df = 4, null.model = F,
  grid.size = NULL)

plot3d_genes(data, genes.subset, low.dim)

`data`	a `warpDEDataSet` with results to be plotted.
`ranking`	a `rankingDE` object, rankings rows of the genes of interest in the ranking dataframe.
`genes.subset`	character vector, let the user specifies the names of the genes of interest (default is NULL).
`order`	character, "head" (default), "tail" : specify if we want to see the `nb.show` first or last genes of the ranking.
`nb.show`	numeric, number of genes displayed if genes.subset = NULL (default is 8)..
`reg.f`	a function to perform regression, either "ns" for natural splines, "loess" or "splines" (default is "loess").
`span`	numeric, a smoothing parameter for the regression function (default is 0.75, see `gam::lo` for details).
`s.df`	numeric, a smoothing parameter for the nsplines regregression (default is 4, see `splines::s` for details about regularization).
`null.model`	logical, if the plot of null model is wanted (default is FALSE).
`grid.size`	2 by 2 vector, for the number of rows and the number of columns that we want for the plot (the size of grid must #' be greater than the number of genes of interest), default is NULL for a squared grid.
`low.dim`	array, a 3D dimensionnal representation of the scRNA-Seq data. We expect an array of dimension (N x 3) where N is the number of cells in the experiment.
`data`	a `warpDEDataSet` with results to be plotted.
`genes.subset`	character vector, let the user specifies the names of the genes of interest (default is NULL).