New wiki page to document potential models

[ndphillips]

I created a new wiki page here (https://github.com/mdsteiner/GoalDirectedDecisionMaking/wiki/Potential-models-of-goal--directed-search) to document existing and potentially new models of goal directed reinforcement learning.

I think this would be a good place to keep track of ideas we have for models :) In the mean time, I've added a description of the model we discussed in the past which seems more psychologically plausible than the one we used in your Master's thesis.