newGmm: newGmm
In VBmix: Variational Bayesian Mixture Models

creates an empty GMM data structure.

newGmm()

list object with the following members:

`w`	numeric vector containing the component weights of the mixture model.
`mean`	list with respective means (numeric vectors) as elements.
`cov`	list with respective covariance matrices as elements.
`a`	constraints between components, encoded in a numeric vector. One value per component. 2 components associated to the same value are said to be from the same origin. Used in vbconstr.