End Game Handling

#### What's this PR do?
`getNextLevelMessage()` is added to handle what messages to send users after the end of a level. This also includes the end game message which would come after the last level.

#### Where should the reviewer start?
It looks like there's a lot going on here, but there really isn't. The majority of SGCompetitiveStoryController.js is just cleaning up the tabbing on the `if (typeof nextOip === 'string' && nextOip.match(/^END-LEVEL/))` block. The only real new thing is `getNextLevelMessage` which basically just reuses the `getEndLevelMessage` logic to figure out what the end-game message should be.

#### What are the relevant tickets?
More for #73