Graph Editor : Add snapshot capability

[kwokcb]

Changes

Fixes issue #2429

Add in "snapshot" capability for node editor panel.

Interface Changes

New Keys

• CTRL-I : capture the editor panel
• CTRL-SHIFT-I : capture the entire window

Help Dialog Update

Each option will bring up file dialog to allow user to input file name to save. Defaults to PNG extension.

Examples:

Example	Snapshot
Top Level
Inside Graph
Entire Window