Decouple the AdobePdf module from ScholarSphere

[ajkiessl]

It might be useful to have this as its own gem so it can be used elsewhere. It should be pretty close to decoupling. Any place that invokes AccessibilityCheckResult.create! can be replaced with either the returned report or an error. File handling will likely need changed. The S3Handler module requires a FileResource, which binds it to ScholarSphere. Perhaps just handing it an S3 key, or file path would be better for decoupling?