This addresses #6543 by adding an option to prevent fonts such as Palatino and Times to automatically adapt the math font (IOW it lets you load the text font only for a bunch of fonts where this is easily possible).
Furthermore it adds an interface to select a specific math font, which is defined in latexfonts. Currently, this is only euler (the only one I know), but if there are other math-only tex fonts, they can be added easily (but note that this changes the file format).
Non-TeX math fonts are not yet supported. Eventually, unicode-math support can use the existing UI, but this is not on my agenda.
The LaTeX font now do not specify simply alternative packages or packages for OT1 encoding etc., but they refer to complete AltFonts (which are not directly accessible via the GUI). This way, alternative fonts can also have options (osf, sc etc.), and they can use all sorts of initializing methods (\usepackage, \setrmfamily etc.).
The LaTeX font information are now centralized and outsourced. This removes a lot of hardcoding and duplication and makes it easier to support new LaTeX fonts.
