Named `FormulaEquationInput` (name up for debate)
-For the initial pass, just copy off of ChemEqnIn
-Add FormulaEquationInput in inputtypes.py
-Add a call to a skeleton method for a preview

javascript:
-Queue up some MathJax
-Put some ordering on the AJAX requests: add a parameter when the request was started, when it returns check that it isn't outdated before displaying the preview