Fixed: table view selection color did not change when losing focus.

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.

Fixes #1839
Fixed: table selection highlight gradient top/bottom too dark.

In CPTableViewSelectionHighlightStyleSourceList selection style, a table view draws the highlight on each row with a top line, linear gradient, and bottom line. Previously, the top and bottom lines were quite dark in relation to the gradient.

This commit makes the top and bottom line brighter, to make the transition to the gradient more subtle.

Refs #1839
Fixed: unfocused selection highlight in table upside down.

Previously the gradient in an unfocused selection highlight in CPTableViewSelectionHighlightStyleSourceList style was darker at the top and brighter at the bottom, which is the opposite direction of the gradient when focused.

This commit makes all of the unfocused highlight colors a strict 5% desaturation of the focused colors.

Refs #1839