Add loadFileRequest and fileManager infrastructure

[swederik]

See https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!topic/cornerstone-platform/e3JAt5cIUtM

We should be able to load images from file inputs as we can with the WADO Image Loader.

[swederik]

Brought up again: https://groups.google.com/forum/?nomobile=true#!topic/cornerstone-platform/PruwQ9fW_qA

[nisalupendra]

I believe there should be a way to load images from blob urls. It's not always possible to serve medical images from a file server due to privacy concerns.