Populate csv files within a folder to populate a sport with players, part 1

@ShaiNirShado 

This one gets the most basic functionality that we're looking for. It goes through all csv files in a folder at the root called ```default_players```, then it'll go through the columns as necessary and add them to the database, and add them to the proper sport id. (Format for CSV files are written in the comments).

Next up on the list is to manipulate strings in the csv so this process isn't so troublesome where we have to manually edit all the csvs to this format, and to label rookies. 

As for the other PR, can probably safely close that one (it's mainly for review purposes), but I was wondering if we should just run this populate method when we create the new sport?
We might want this error message to give more information -- for example, give at least one player name and print the error details so that somebody reading the error logs knows which row of which file is causing the problem.

Incidentally, last week I added a simple global error logger that writes errors to a file. It might be better to plug that logger in here post-merge since Heroku doesn't save console logs by default.