Grade distribution calculator

[tylerhou]

There was some discussion in my class's Piazza group about being able to put in standard deviation + median information about a test and have BerkeleyTime predict a grade.

Potentially we can support multiple tests with weightings. For each test, you could enter your score, the standard deviation, the median, and the weight. Then BerkeleyTime would take the sum of all distributions weighted by the weighting and predict your grade based on historical data.

I think it would make sense to put this on the grades page, but maybe that would be too crowded.

We would also have to fix #470.

[hi-usui]

To comment on this: Moving forward, the proposed new backend is going to focus on returning raw data, and we'll hand it off to the React client to do basic statistical calculations. This way, grade distribution calculations becomes more transparent and it opens up the project for more suggestions.