Display user names the same everywhere

[violine1101]

Purpose

Display new user handles as @violine1101 and old ones as violine1101#8993 everywhere.

This also should fix the issue where messages could not be deleted if you had a new user handle.

Approach

Add a helper function in DiscordUtil to decide how to print the name. Also added two more helper function for consistent setting of embed footers and authors.

Future work

We'll probably need to rework this with the next discord.js update anyway, I presume (though I haven't checked their progress on the matter)