add getUniqueIndivEndGameMessage function, test JSON files

#### What's this PR do?
Adds new endgame logic to provide individual users messages indicating their rank. Ties for first and second place are possible. 

#### Where should the reviewer start?
The reviewer should start by looking at the way in which the gameConfig data structure in test-endgame-message.json has changed. I've included two new objects: 'indiv-level-success-oips' and 'indiv-rank-oips'. 

#### How should this be manually tested?
**I'll continue to test this new functionality for 3-4 player tie conditions.** Note that in order to test, the reviewer needs to change the gameConfig file loaded at the top of the competitiveStoryController to the `test-endgame-message.json` file.

Note that I've included two new test JSON files, which are the completed gameDocs for two situations: a) where two players both pass six levels with the success condition, resulting in a tie; and b) where the first player passes six levels and the second player passes two levels. 

I've included these files for hacky unit testing of the function--I've been testing the individual function on a REPL.

Further testing should be done end-to-end with POSTMAN. 

#### What are the relevant tickets?
**JIRA** SMS-60