feat(BaseListbox): allow value prop as model with v-model.prop

[JohnCampionJr]

I need to use object ids in my listboxes, so I added this feature. Thought it'd be a nice addition.

Also added a test page to verify this works as expected.

I coded it as a non-breaking change.

[stafyniaksacha]

Hello @JohnCampionJr

Thanks for the contribution, it's a good feature, we will add it to next release!

I would change it a bit to use model modifiers, so we can use it like <BaseListbox v-model.prop="" /> instead of having a boolean property (like in BaseInput here and here)

[JohnCampionJr]

That's a nice tweak, I'll do that :)

[JohnCampionJr]

All set!