Widget Editor

[ericmehl]

This adds a new editor for inspecting (and someday, actually editing) widget properties in the UI. I've been working on it on Friday afternoons for a bit now - it's not done by any means, but I think it's worth having a look at the current state to see what we think about the direction it's going in and how the basics are working out.

Currently it can :

• Browse the hierarchy of widgets starting with the script window children.
• Let the user pick a widget with the mouse and focus on that widget in the hierarchy.
• A variation on picking widgets where the picker waits 3 seconds to activate in case you need to open a menu or similar.
• Highlight the selected widget in the UI with a blue overlay.
• Drag and drop into the Python editor to get code for identifying that widget.

Here are a few items I have on mind for discussion :

• How to expose the editor. Currently I have it as a registered editor you can add to a layout (but not part of any default layout). Is even that giving it too much exposure to users who will likely never need it and may be confused by it?
• How to allow editing since the values are not plugs. I'm thinking custom columns as needed that respond to double clicks by popping up a NumericWidget, but haven't started to implement this, maybe there's a better solution.
• Add other properties.
• Allow changing the root window to something other than the script window so you can inspect widgets in a dialog box.

Checklist

• I have read the contribution guidelines.
• I have updated the documentation, if applicable.
• I have tested my change(s) in the test suite, and added new test cases where necessary.
• My code follows the Gaffer project's prevailing coding style and conventions.