Buttons to add users with uuid and username should auto get uuid

[Daniel Jørgensen]

When adding a user to white / black list or as an operator, a button should be present to automatically get the UUID based on the username via mojangs official player profile API

https://api.mojang.com/users/profiles/minecraft/<username>

[Daniel Jørgensen]

Implemented automated UUID AJAX retrieval and more work on new design. fixes issue #2

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