Combine array of elements when typesetting

Currently, MathJax.Hub.Typeset() and its brethren accept an array of containers whose contents should be typeset, but it handles each as a separate typeset call. These should be combined in order to take advantage of chunking and prevent unwanted reflows. The worst-case scenario is when the array is of individual elements that should be typeset, as this would force reflows between each equation.

Instead, the expressions from all the elements in the array should be combined into one list, and that processed all at once in order to take advantage of the optimizations for multiple expressions.