getLNormFactors: Get log-normal factors
In JINJINT/ESCO: Simple Simulation of Single-cell RNA Sequencing Data

Randomly generate multiplication factors from a log-normal distribution (this function is borrowed from splatter).

1	getLNormFactors(n.facs, is.selected, neg.prob = 0, fac.loc, fac.scale)

`n.facs`	Number of factors to generate.
`is.selected`	whether a factor will be selected to be different from 1.
`neg.prob`	Probability that a selected factor is less than one.
`fac.loc`	Location parameter for the log-normal distribution.
`fac.scale`	Scale factor for the log-normal distribution.