Added an ImageStats node to the image viewer so that the user can Shift-LeftMouseDrag a sample area within the image and view it's statistics.
When a sample box is visible the user can drag colours from the swatches into the terminal.
Changed instances of "Colour" to "Color".
Fixed bug when right clicking a non-DependencyNode node in the node graph.
Added optional Menu titles.
Added title to PlugValueWidget popup menus.

The title disambiguates the context in which the menu items below will be executed.

Fixes #265.
Merge pull request #362 from goddardl/ImageStats

Added sample window to the ImageViewer.
Changed version to 0.67.0 and updated Changes file.
Fixed menu title so it doesn't interfere with menu keyboard navigation.
Merge pull request #373 from johnhaddon/plugMenuTitle

Plug menu title
Removed right-click layout context menu.

It can now only be accessed via the layout button.