feat: Add button warning log for modal-footer button count

If more than 3 buttons are found in the modal-footer slot, a console warning is thrown with the message Warning: The modal footer should not contain more than three button elements. There are currently ${count} buttons.

As far as the autofocus helper goes. I looked into it and found out Bootstrap already has an easy way for developers to set focus on a certain element. See here for more information.

Closes #288 (closed)