Dino Dex First Refactor

Let me know when you have a few minutes.  I want to go over a few of the questions you had which I haven't yet done anything with.
This method returns the period type so no need to assign it to `@period_type`. Just do:
```def period_type
  PERIOD_PERIOD_TYPES[period]
```
Not sure why there are two PERIODs in the name of this hash.