Default Tile title tag to 'p' when description is empty

Careful to not put a slot inside an HTML p element.

Unfortunately, browsers may move the slot content of the p element if there is an unexpected markup in it.

@pdureau Although I think I understand your statement, I believe this issue requires a lighter modification than expected ^^?

I will have look, thanks

Is the switch to 1.1x the opportunity to deal with this?

Let's discuss this for 1.1.x branch.

title is a slot. Do we move it as a string prop?
in that latter case, it can be safely put inside a p tag.