Add API call for looking up screenshots.
Speed up screenshot search query.
Create new comparisons and screenshots via the API.
Handle case when a screenshot already exists.
Reference a specific screenshot version from comparisons.
Remove screenshots from API.
Always create screenshot with a version.
Add method for retrieving current screenshot version.
Move logic for comparing images to screenshot model.
Add JSON response for creating comparison.
Merge pull request #15 from bradgignac/api

API