Fixed: table view selection color would not change when not firstResponder

CPTableView has no focus ring, and currently gives no visual feedback of its firstResponder status. In Cocoa when the table view resigns firstResponder or its window loses key status, the selection color turns gray.

This commit sets the selection color to gray when a table view resign firstResponder or its window loses key status. A second window and a couple of textfields were added to the CPDictionaryControllerTest to demonstrate the changes.