-Add API information link at the top of Pushbullet.cs
-Readability/consistency improvements for Pushbullet.cs;
-Update FileUpload code in Pushbullet.cs to work with v2 of the PB API;
---Add new serialization objects for file upload request responses;
---Add more null checks since null responses may be more likely now;
-Remove unnecessary response data from old deserialization objects;
-Add Pushbullet as a URLSharingService (it is :D);
-Change classes from public to private;
-Move Pushbullet entry to FileUploaders in UploadersConfig.cs
Merge pull request #261 from BallisticLingonberries/master

Updated Pushbullet to use PB API v2, and added PB as a URL sharing service