Replace use of debugPrint with NSLog.
Add notification name for a changed scheme.
doc: Add observer for changes to its scheme.

Used to update the change count for the document.
Add scheme properties to selector table controller and data source.

Controller updates the data source's property.
doc: Update the selector controller's scheme upon change/load.
rulesData: Notify the scheme has changed for successful drops.
colorController: Notify the scheme has changed for color changes.
Notify the scheme has changed for selector changes / drops.
Use the sender instead of named color wells.

Too many opportunities for screwing up when it's already known that the
sender is that color well. Skips potential typos as a result.