Add #FeesMustFall storyline to choose-your-own-adventure

[maoivy]

• Added all currently-written stages from the doc
• Added a new 'showOnEnd' field to every option
  • This is to distinguish the 'Next' option on intermediate slides without real choices from the actual choices
• Removed successFactor and numeric calculations
• Changed text from strings to divs to accommodate formatting
• Things that appear as a result of cumulative choices (as opposed to one single choice) are handled as variations of a stage (e.g., people who chose not to do nothing for the sit-in see STAGE_2, people who chose to do nothing for the sit-in see STAGE_2_1C)