1.21.0 / 2017-10-17

* Fix Android O compatibility issues
* Implement cancellation for in-progress requests.
* Sample app improvements and fixes.
* Add signing to gradle build

New functionality

-----------------

  * Add new **MediaManager framework**
    * Upload scheduler
    * Upload Policy
    * `ListenerService` and `UploadCallback`
      * `onStart`
      * `onProgress`
      * `onSuccess`
      * `onError`
      * `onReschedule`
  * Move Cloudinary Android SDK back to cloudinary/cloudinary_android