Well, I just spoke to Vivek with Adobe, and it LOOKS like they will be putting the extension panel functionality back, or the deprecated behaviour panel back. Not sure... this is what I was told:
Vivek: I apologies for the inconvinience.
Vivek: This is a known issue with Dreamweaver CC 2015 update and engineers are working on top priority for that.
Vivek: In the meanwhile I would advice you to download Dw Cc2014.1 to use the deprecated panels.
Jules: How do I do that?
Vivek: Link above shows the exact steps for that.
Jules: OK... I have looked. I will do that. Are they removing all of the extension panel for good?
Vivek: Its removed by some glitch but it will be fixed soon.
Vivek: then you will be able to use them in DW CC2015
Jules: OK... thank you! Whew!