Refresh MathJax if necessary

[Carifio24]

This is an attempt to resolve #519. It's seemed to work for me so far, but some of these issues have been a bit flaky so I'd appreciate another look.

[patudom]

Still not working for me. The slideshow behaves differently when you are going through for the first time in that stage vs. if you've already entered in the speed of light in a prior run on the slideshow. If you've done the slideshow once, your speed of light is stored in the db (even though it appears blank on the 2nd to last slide of the slideshow), and when you get to the last slide, MathJax already has your speed of light value and works correctly.

If you refresh your stage state and go through the slideshow for the first time, the original pass of MathJax still has 0 as the speed of light and I get variations of this. (Note if you refresh the stage state, you will have to remeasure the observed wavelength on marker obs_wav1 otherwise the db will have that stored as 0.)

[patudom]

See above comment