NA strings field for formats record

[bcow]

Add a text field to BETY formats that stores NA strings separated by commas.

Maybe something like this?

class AddNA_stringsformats < ActiveRecord::Migration
  def up
    add_column :formats, :NA_strings, :text,  :null => false
  end

  def down
    remove_column :formats, :NA_strings
  end
end

[dlebauer]

@bcow could you submit this as a pull request?