Add problem catalog

[hljeong]

There are approximately 0 high quality Kattis problem catalogs on the Internet. We can make the first.

I envision a filterable problem catalog with tags (topics, platform, difficulty). Problems can also be tagged with which UCLA ICPC trainings they showed up on. This will help with training set setting since we will know which problems are good and when they can be recycled.

Further down the line we could even have officers, team, and general members write editorials for select problems. Editorials seem to have been a recurring incentive but have always failed. I can but dream for the day of a prosperous and self sufficient competitive programming community at UCLA.