refactor(CRaterRequest): Create AbstractCRaterRequest

[hirokiterashima]

Create AbstractCRaterRequest that implements CRaterRequest interface. CRaterScoringRequest and CRaterVerificationRequest will both extend AbstractCRaterRequest.

Extract these common fields and method:

• String itemId;
• String cRaterClientId;
• String cRaterUrl;
• public String generateBodyData() throws JSONException

Make sure that everything works as before for C-Rater tasks

[hirokiterashima]

This was completed in #289