FIX - Cordova File does not inherit from Blob.
FIX - Cordova File does not inherit from Blob.

* Particular fixes for Cordova when a File is used.
* Minor code cleanup for clarity.

NYPL-Simplified/readium-shared-js,NYPL/readium-shared-js,JoMedia/readium-shared-js,pmstss/readium-shared-js,NYPL/readium-shared-js,readium/readium-shared-js,ravn-no/readium-shared-js,AccessSeoul/readium-shared-js,kivuto/readium-shared-js,readium/readium-shared-js,NYPL-Simplified/readium-shared-js,kivuto/readium-shared-js,AccessSeoul/readium-shared-js,ravn-no/readium-shared-js,pmstss/readium-shared-js