Remove the CsvHelper (and fastercsv) and use stdlib CSV

Following instructions left at https://github.com/ferrous26/Markus/blob/9e03a6bd9de6a12a12b0f399d96b5c31e673b2c6/app/helpers/csv_helper.rb, I removed the `fastercsv` gem and the wrapper around CSV libraries. Though, since `csv` is used extensively, I added the `require 'csv'` line to `config/boot.rb` so that it is always loaded instead of putting it at the top of various files.

Testing done:

- `rake test`