Maximization step of the algorithm

Use the expectation step to generate parameters of the mixture model

maximization_step(pca.components, clusters, parameter.estimates,
  posteriors, num.cores)

Arguments

pca.components	Expects a matrix with n rows as the cells and m columns as the principal components.
clusters	Expect the most likely cluster assignments.
parameter.estimates	Expects a list of parameters (mu, covariance, and weights) from initialize_gmm or maximization_step.
posteriors	Data.frame of priors from the expectation step.
num.cores	Number of cores used for parallel calculations