Allow a title bar to be resized smaller than its width.

If a title bar becomes smaller than its width (the sum of widths of all its
icons) use an extension button to show hidden buttons.
Note that the title bar is as small as before but there is some space
between the title bar and the extension menu (when that appears).
It seems this is because the tool bar wants to be a certain size.

Change-Id: I53a019505937462c8aba20edb5c17df720a19e9e
Remove vtkSESAMEReader.

vtkSESAMEReader is not used by Prism, we have new class vtkPrismSESAMEReader for
it.

Change-Id: Ia973ca9e4b026da30bef96de191abc7129e6943b
Merge topic 'remove_sesame_reader' into next

36a27bb Remove vtkSESAMEReader.
Merge topic '14368-toolbar' into next

2be288f Allow a title bar to be resized smaller than its width.