This reverts commit acfd0d9f, reversing
changes made to e4194c99.

This reverts commit 57427f9a, reversing
changes made to 37621c26.

Added support for superscripts in variables and fixed bug with normal subscripted variables raised to powers

symmath_check for simple symbolic input strings.

the expected result = 0.  symmath_check() was dividing
a quantity by the expected result, leading to a NaN value
that caused the answer to be marked incorrect.

Added test_symmath_check.py with basic tests for
the symmath_check() function.

evaluated bool(ans), which is False when ans=0.
This led to an error message "[symmath_check] failed to get MathML for
input; dynamath=[None]" when the function reached a later condition.
The check that evaluated  bool(ans) was redundant, so I removed it.

Make type check for self.code a little more robust, give default val for mmlans so it's never undefined

This reverts commit e4819a1b, reversing
changes made to b6ec41ca.

Now that we're ready to test again, need to revert the revert to put the filtering UI back in.

This reverts commit 66889b87, reversing
changes made to 0dd9c24e.

This was merged too early--it's still missing the filtering and display-your-cohort changes.
Will need to revert this revert later.