Changed timeline behavior to scroll selected entry to middle when next selected entry isn't visible. Issue #604

NetNewsWire/MainWindow/Timeline/Keyboard/TimelineKeyboardShortcuts.plist

@@ -2,6 +2,18 @@
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <array>
+	<dict>
+		<key>key</key>
+		<string>[uparrow]</string>
+		<key>action</key>
+		<string>selectNextUp:</string>
+	</dict>
+	<dict>
+		<key>key</key>
+		<string>[downarrow]</string>
+		<key>action</key>
+		<string>selectNextDown:</string>
+	</dict>
 	<dict>
 		<key>key</key>
 		<string>[leftarrow]</string>

NetNewsWire/MainWindow/Timeline/TimelineViewController.swift

@@ -253,6 +253,51 @@ final class TimelineViewController: NSViewController, UndoableCommandRunner {
 		NSPasteboard.general.copyObjects(selectedArticles)
 	}
 
+	@IBAction func selectNextUp(_ sender: Any?) {
+		
+		guard let lastSelectedRow = tableView.selectedRowIndexes.last else {
+			return
+		}
+		
+		let nextRowIndex = lastSelectedRow - 1
+		if nextRowIndex <= 0 {
+			tableView.scrollTo(row: 0, extraHeight: 0)
+		}
+		
+		tableView.rs_selectRow(nextRowIndex)
+		
+		let followingRowIndex = nextRowIndex - 1
+		if followingRowIndex < 0 {
+			return
+		}
+		
+		tableView.scrollToIfNotVisable(index: followingRowIndex)
+		
+	}
+	
+	@IBAction func selectNextDown(_ sender: Any?) {
+		
+		guard let firstSelectedRow = tableView.selectedRowIndexes.first else {
+			return
+		}
+		
+		let tableMaxIndex = tableView.numberOfRows - 1
+		let nextRowIndex = firstSelectedRow + 1
+		if nextRowIndex >= tableMaxIndex {
+			tableView.scrollTo(row: tableMaxIndex, extraHeight: 0)
+		}
+		
+		tableView.rs_selectRow(nextRowIndex)
+		
+		let followingRowIndex = nextRowIndex + 1
+		if followingRowIndex > tableMaxIndex {
+			return
+		}
+
+		tableView.scrollToIfNotVisable(index: followingRowIndex)
+
+	}
+	
 	func toggleReadStatusForSelectedArticles() {
 		
 		// If any one of the selected articles is unread, then mark them as read.