[UploadController] Response now includes a raw_url field

[cursey]

I have sharex configured to add /raw to the end of every uploaded file automatically but that results in broken .gif thumbnails in discord and requires extra configuration steps.

This change just includes a properly formatted raw_url field in the /upload response that can be used more easily from sharex and creates working gif thumbnails in discord.

Note: The broken gif thumbnails in discord seems to be entirely discords fault. I think they're just looking at the URL and seeing if it ends in .gif which is why this change fixes that behavior.

[angelfor3v3r]

I tested this out on an instance I'm running and it does indeed fix my issue at #493. The only thing I had to do is change my ShareX config to read the raw_url instead. It seems like certain sites/apps specifically look for extensions + a raw site (i.e. without the XBackBone interface). The "copy raw url" mode exists which does exactly this, I guess it only makes sense to have it available in the API too? Perhaps down the line an option in the user settings page to generate the ShareX config with this in already set would be nice, too.

Closes #493