add React leaderboard/Hall of Fame

[nijynot]

Fixes mimblewimble/grin-pm#52.

• To add a new donation to the leaderboard/Hall of Fame, insert a row to income_log.csv. Total, last donation, number of donations, and the "dropdown history" will be automatically updated from that.
• If a new company/individual is being added to the leaderboard, don't forget to add them to the entities.csv (currently in assets/csv/entities.csv) file too. Editing the description, name, profile image or link of a company/individual is done in entities.csv.

One caveat is that the "name" (source in income_log.csv and name in entities.csv) must be the same when referenced. It's case insensitive, but does not trim whitespace.

Threshold for showing up on leaderboard is $25,000, so it'll be empty as of now.

[lehnberg]

This looks great @nijynot thanks a lot for this! I've not tested it in action but took a look at the HTML and CSV structure of entities.csv, great job. Once merged I can add more info about the leaderboard and how it works on the page itself. 👍

[garyyu]

Thanks @nijynot, this implementation is awesome 👍 😃
Let's start using this nice Hall of Fame feature :-)