Error highlighting broken in non-Chrome browsers

[longouyang]

We need to implement custom stack parsers to handle non-Chrome

[longouyang]

Update: It doesn't look like this will work in Safari, as its error locations are totally wrong (it doesn't do a good job when errors happen in eval'ed code).

Firefox looks a little better but the locations are somewhat off and would be pretty annoying to resolve.

I think it makes more sense to try to solve these issues by manually constructing a webppl stack trace in the trampoline runner, as suggested in probmods/webppl#314