Resolve "evaluate math expressions"

Goals

This MR will add functionality to make questions that allows users to enter a math expression instead of a single value as a result.

Non-goals

This MR will not add functionality to execute arbitrary python code.

Implementation

This MR will limit eval to be shut as best as possible. still, in order to even evlauate code, the user has to explicitly set a flag to true.

Closes #64 (closed)