HttpAssetProvider: Make this provider queue completed transfers and feed them to AssetAPI based on how much time they spent for the remaining loading time. This logic breaks once transfers have been served for 16msecs during a mainloop frame, logic is exactly the same as for LocalAssetProvider. Implemented threshold by size logic to perform cache write in the main thread. This logic is currently disabled by making the threshold 0 (everything async) but is there for easier debugging for profiling reasons. As noted in the pull request discussion even opening a file can block big time even if the write operation would be quick etc.