Filter scoreboard by event tag

[r2dev2]

For PBR CTF, we will have challenges specially released during the PBR meeting. However, with the current scoreboard system, we can only see score across all challenges and not just PBR CTF challenges.

It would be nice to get a scoreboard for specific event tags. For example, I could be able to check all the filter tags on the scoreboard page and see the scoreboard for challenges matching those tags.