Support tracks to compare classes of fuzzers (binary-only, source-only, hybrids, etc)

Thanks for maintaing an awesome project!

I am writing to discuss my concern about the unfairness of fuzzbench results due to the difference between binary-level vs. source-level fuzzers/

When I look at the current [sample report](https://www.fuzzbench.com/reports/sample/index.html), all the tools used here except Eclipser run with source-level instrumentation (with afl-cc). Eclipser, on the other hand, uses QEMU to instrument binaries.

It is well-known that binary-level instrumentation incurs significant overhead (several orders of magnitude) compared to source-level instrumentation. Therefore, comparing Eclipser with source-level fuzzers, e.g., AFL, is not entirely fair as they have different goals and uses. However, comparing Eclipser with AFL running in the QEMU mode (-Q option) would be fair, for example.

So I would like to suggest separating tracks in fuzzbench into two: binary track, and source track. In the binary track, we can include AFL-QEMU, Eclipser, VUzzer, etc. I believe showing two sets of graphs for each program would be enough. For your information, having multiple tracks in comparing tools is a common practice in other domains. For example, SMT-COMP currently has 6 tracks: https://smt-comp.github.io/2019/results.html.

This way, people can appreciate more about binary-level fuzzing research 😄 I truly believe this will benefit our community as well.

Thank you!