Add support for displaying median benchmarks

[str4d]

Includes:

• A new type field to benchmarks to distinguish between mean and median data.
• New result fields for storing Q1 and Q3.
• Toggles for displaying quartile and extrema bands on median benchmarks.

See this graph for an example.

[tobami]

We could factor out the data formatting somewhere common to both data_types. Even a method on revision date_formatted() or similar

[tobami]

Wow, this looks awesome! Can you please add a screenshot to the PR description? Even better would be to expand codespeed/fixtures/testdata.json (or codespeed/fixtures/testdata.json) so the sample data shows the new type of benchmark data.

In any case it looks great!

[tobami]

Another thought: it would still be useful to be able to show min/max even if the benchmark is of type mean. Could we still show the checkbox even in that case?

[str4d]

It's certainly possible, but it would either require duplicating code or some more refactoring. Probably duplicated code would be easiest, since otherwise the parsing code would not be single-pass, which would be less efficient for larger datasets.

It may be easier to do that once this and #204 are merged (so then the refactor can also tidy up the general handling of extra options). I don't personally need it, so I can't promise I'd get it done (because I can't put company time to it), but if done with duplication it's a simple-enough change that it shouldn't take me long.

[tobami]

Al-right! Let's get it merged then, thanks.