[cla][patch][test]TitlePane not easily subclassed

[nathan]

TitlePane? is not very easily subclassed - since the _setCss function operates on focusNode. The end result is that a subclass cannot move focusNode off of the title bar (although, it may be desirable - for example, to have *ONLY* the arrow be the focus node).

In the included patch is a test case (in the form of a patch to tests/test_TitlePane.html) that demonstrates moving the nodes around.

The suggested fix is to create a new attach point (called, in this patch "titleBarNode") and use that node for the _setCss functions.

[guest]

Allows the focusNode to be moved, if desired.

[guest]

Patch submitted by Nathan Toone

[bill]

(In [12697]) Fixes #5973: make TitlePane? more easy to subclass by separating out titleBarNode and focusNode as separate attach points. Patch from Nathan Toone (CLA on file)