Markup Features Implemented: Add Researchers, Assign Markups, Assign Interrater

Documentation in markup.rake:
 Notes: These commands will take time to execute based on total number of katas.
        There is no overlap of assigned kata sessions between researchers
        or between individual assignments and the interrater sessions.

 Usage:
   bundle exec rake markup:assign_markup [KATAS=#]
     Assigns random katas to each researcher with no overlap
     May optionally specify # of Katas (do not include the square brackets)

   bundle exec rake markup:pick_interrater [KATAS=#]
     Assigns random katas for the interrater agreement
     May optionally specify # of Katas (do not include the square brackets)

   bundle exec rake markup:add_researcher NAME=name
     Adds a new researcher with the name provided, if existing researchers
     currently have assigned katas, the same number of katas will be assigned
     to the new researcher.

I wrote it this way so that it would be easy to add or remove limits as desired. While it does take a little bit to execute, in my testing it never took longer than 30 seconds for any of these commands using the entire dataset so I'm not sure optimization is necessary since we only will run these a couple times at most.