Evidence attachment system

[gdude2002]

Our infractions system should include a way to attach evidence to infractions. After #13 is implemented, action logs will be rotated automatically - which means we need to attach offending content to infractions before the context for those infractions is lost.

Ideally, this system should meet the following requirements:

• Allow attachment of screenshots and other files to infractions
• Allow for the attachment of on-server data (for example, messages)
• Optionally, allow attaching an action log message (for example, a deleted message log) - we don't store these in the database so they will have to be parsed from the message on Discord directly