JDK-8200587: Fix mistakes in FX API docs

[Nir Lisker]

Hi all,

Iv'e created another issue for collecting JavaDoc corrections:
https://bugs.openjdk.java.net/browse/JDK-8200587. If you found any, please
add them to this issue and I'll fix them along with what's there already.

Kevin,

* Different items on the list affect different versions, but they are all
relevant for the latest 11ea build. If there are plans to backport they
would need to be sorted out. One of them is a regression from 8 (in
Dialog), but it's trivial.
* I collected 2 recent issues into this one (links in the issue), so should
I close them as duplicates?

Thanks,
Nir