Ability to assign icons to user groups

[NateDhaliwal]

@long I think I managed to do it.

https://github.com/NateDhaliwal/add-custom-icons-to-username

Note that if the user is in 2 groups where both are in the settings, the first one in the settings takes precedence.

Settings are pretty self-explanatory:

Please report back if you have any problems!

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Note that this is just a proof-of-concept. I will not be maintaining this forever.