feat(upload): Client Side S3 upload

[pratik60]

Wondering if this is in the roadmap....

[valorkin]

hm

[tdonohue]

Note, for Amazon S3 support (or other APIs which expect just streaming the file), you may need an option for disabling multipart form encoding.

See this parallel effort in angular-file-upload (Angular1) nervgh/angular-file-upload#602
and the related S3 corruption issue that it solves: nervgh/angular-file-upload#382

[tdonohue]

Note: #224 should allow you to upload to Amazon S3 using pre-signed URLs. It's essentially the same fix that was applied to angular-file-upload (for Angular 1) as noted above.