Implement `rank_initial_prompts` for web

[fozziethebeat]

The rank_initial_prompts task type needs to display these fields:

• prompts: An array of prompts

It takes the following interaction type:

• type: post_ranking
• ranking: An array of ints representing the preferred ordering of the prompts, indexed by zero. example: [2,1,0,3] for a series of 4 prompts.