Mathtype implementation

This MR adds conversion of MathType binary files to LaTeX equations.

MathType is a proprietary equation editor used in MS Word; documents that have MathType have binary .WMF files. A Ruby gem made by Jure ( https://github.com/jure/mathtype/tree/master ) which was then brought into XSweet by Suki ( https://gitlab.coko.foundation/XSweet/XSweet/-/tree/mtef/applications/math/mtef ) is run on .wmf files if any are found in the unzipped files. If they exist, we try to convert them to LaTeX (via MathML) and replace the images in the html with <math-display> or <math-inline> LaTeX equations.

Note that this doesn't work for all WMF files – not all WMF files are MathType. And it seems possible that Jure's gem doesn't actually work for all flavors of MathType.