Support uploading of InputStreams

[shawnmaten]

We need to be able to upload from InputStream objects so that we can properly support local uploads in Android. This will require refactoring the Upload* classes a bit. I think the main issue will just be rethinking how we divide the work between multiple workers. Right now we assign a (worker / thread / observable) a section of a file to read and upload. Instead we should have multiple workers that independently read and upload from a shared InputStream. That reading will have to be synchronized, but otherwise I don't think this will be too much of a problem. To keep support of uploading with a file system path, and not overcomplicate things, we should just convert file system paths to InputStreams.