Added option to exclude user/bot avatars from file encryption

[crispyross]

Adds an option (Common.encryptAvatars in src/common.js) for whether to include or exclude user/bot avatars in the file encryption system used in Common.mkAndWrite. This allows for serving the avatar images with a plain HTTP server rather than having to involve middleware to decrypt them.

[CampbellCrowley]

Ah I totally forgot about this, thanks for adding this in!

I had thrown data encryption in very quickly because I am required to have it by the Discord TOS for "API Data". However it's a little confusing on whether avatars or NPC images fall under the category of "API Data" as they come from their CDN.
link to TOS TOS Definitions

Any thoughts before merging?

[crispyross]

I would argue that avatars are public info since they're chosen by the user to always be displayed next to them, and are hosted from their CDN, as you said. But I didn't really think about TOS when I made this change -- it was just something useful for self-hosting that I shared.

I'll leave the choice up to you whether you want to merge this option, and feel free to change the default setting to encrypted.