Improve error handling in mathEntryInteraction semantic enrichment

[davemckain]

The semantic enrichment process that attempts to convert raw ASCIIMath into vaguely meaningful Content MathML sometimes hits on unplanned corner cases and ends up throwing a logic exception. It would be nice to intercept these so that we can log the offending input with a view to improving the semantic enrichment process (which actually lives in SnuggleTeX). It would also be useful to make sure that these errors propagate to the client in a suitably sane way.