Does it amount to plagiarism by supervisor?
As far as I understand the situation, it seems to me that your advisors' behavior is borderline, even if likely on the wrong side of the border. Since it does not look like a very clear and frank misbehavior, even if you are perfectly right it would be tremendously difficult to prove it beyond doubt. In case of doubt, you could end up being seen more as the trouble maker than as the one who came up with that great idea; the surrounding people to whom you could complain (department head, etc.) would hesitate a lot to go against tenured faculty when the misbehavior is not crystal clear, etc.

With this in mind, I would strongly advise you not to confront to wildly with your advisors. You can (and should, as advised by Shion) discuss with them the fact that you are uncomfortable with the way they presented things, with the use without permission of your slides, and so on; but always let them a way to discuss it calmly. If they feel cornered, there will be little chance of the situation not degenerating into a conflict, and it would be very difficult for you to survive professionally a conflict with your advisors.

You could cite their perspective paper in a way that friendly makes explicit that the idea is yours. Your aim should be to get decent credit for your idea, even at the cost of letting your advisors benefit from it: think about what you have to gain or loose first, rather than about what they have to unduly gain or what you can cost them.

If everything goes smoothly, you can get into a good position to build on your idea, and be on track for your career. 
Once you're a respected tenured faculty, you should remember this episode and be supportive of young researchers.