Make TimelineTableView and TimelineTableRowView opaque in the interest of speeding up rendering during scrolling.

Mac/MainWindow/Timeline/TimelineTableRowView.swift

@@ -10,6 +10,10 @@ import AppKit
 
 class TimelineTableRowView : NSTableRowView {
 
+	override var isOpaque: Bool {
+		return true
+	}
+
 	init() {
 		super.init(frame: NSRect.zero)
 	}

Mac/MainWindow/Timeline/TimelineTableView.swift

@@ -24,6 +24,10 @@ class TimelineTableView: NSTableView {
 
 	// MARK: - NSView
 
+	override var isOpaque: Bool {
+		return true
+	}
+	
 	override func viewWillStartLiveResize() {
 		if let scrollView = self.enclosingScrollView {
 			scrollView.hasVerticalScroller = false