Implement "PB Streaks" Statistic

[dunkOnIT]

From the "New statistic suggestion" email thread:

I’d like to propose the addition of PB streaks to the WCA Statistics page. There’s a wide interest in this statistic in the community and It’s easy to implement as the code for generating the rankings is already on Jonatan’s GitHub page. (Furthermore, but unnecessarily, Antonie is only two comps away from tying Evan's WR)
People might also find it interesting to filter out the ones that finished, leaving only the ongoing streaks as a ranking.
It might be too much to also separate them in continental and national rankings, but that’s up to you.