Implement io.ReadSeeker interface for downloader
Created by: ChrisSchinnerl
This PR adds the /renter/stream
endpoint to the renter which is basically another download endpoint that uses the http.ServeContent
method to serve a resource. This also allows for opening and streaming pretty much every browser supported file in the browser. (also videos).
This is a WIP, contains some nasty caching and disables the Sia-Agent
check to make it work in a browser but I would appreciate some overall reviews.