various latextools fixes

based on #7183

- support unicode text, not just bytes
- remove unused math_to_image copied from mpl
- load global config, instead of instantiating in shell (fixes config load in qtconsole)
- don't unwrap/rewrap math in qtconsole - this broke display of all non-math latex
- mpl math_to_png doesn't support display math, coerce to inline when found