[Feature] Attach files to messages

[Jack-Edwards]

Describe the feature

I think it's confusing for users and a chore for developers to support both "Upload Message" and "Upload File". Instead, I think it would make more sense to attach files to messages, similar to attaching files to an email.

It would be important to make sure uploading a file is still as easy as possible. I don't want users to get the idea that encrypting a file is any less important than encrypting a message. The purpose of Crypter is to make end-to-end encryption easy. I think this is just as much of a UI challenge as it will be a back-end challenge.

Feedback on this is appreciated. What do you think?