* De-duplicate giphy_img? function in favor of a tested service.
Add a tested `GiphyService` and move `giphy_img?` function to it.
Make `labor/markdown_parser.rb` and `models/html_variant.rb` use the service version of the function.
* Refactor GiphyService into Giphy::Image class
Based on comments from @rhymes, I've changed this into a `Giphy::Image` class sincethe repo is currently being moved away from `XYZService` objects for namespacing and organization purposes.
* Fix typo
Update describe case to mention the current method name.
