Revisions to display/layout triggering

• OutlineView now has a `- layoutSubview` override that triggers `- setNeedsPathUpdate`.
• `- setNeedsPathUpdate` now triggers `- setNeedsDisplay`.
	» Removed explicit `- setNeedsDisplay` call from `- setObject:atIndexedSubscript:`.
• ViewController now has an implementation of `- viewDidLayoutSubviews` that calls `- pointsDidChange` and OutlineView’s `- setNeedsLayout`.
	» Removed explicit `- pointsDidChange` call from `- viewDidLoad`.
• New `handleBounds` getter as a named wrapper for `self.imageView.frame`.
	» Switched `- handleCenterFromPoint:` and `handleCenterFromPoint:` to use `handleBounds`.