WIP: Tiny file support

This MR will cause tiny files (<=4kib) to be saved within their corresponding .sia files instead of on the Sia network. It doesn't make sense to store those files online when the metadata required to retrieve those files is as large as the file itself. Instead the data will be stored instead of the metadata on the local disk and uploaded to the Sia network as part of the metadata backups in the future.

Tiny files will always return a 1x redundancy, 100% upload progress and fileSize uploaded bytes.

Resolves #3169 (closed)