Request: Option to style multiple-select items by optgroup

[davidwandar]

I would like to have an option to style selected multiple-select items by optgroup. For example, I have a select with two optgroups "cars" and "bikes". Selected cars get marked with a perticular style (red border perhaps) and bikes with another.

Should be useful in many cases.

[alecarg]

+1 for dropdown-item-and-tag styling for optgroups

[camerond]

I have a pull request open for this here: #591