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.
#