user-logs changes: footers for timestamp, joined message, show nickname instead of tag

[ghost]

• Added a footer triggers the timestamp of an RichEmbed to appear on Android.
• Made the memberJoined log more meaningful.
• User logs use the displayName in addition to the tag so that they some text on Android. The mobile app will show invalid-user when tagging member that isn't in the server anymore, but will show the correct displayName. An exception to this is a banned member, which needs username to be used.

I've tested all events but not the quote command. Does this command make sense anymore?