Clean up the code a bit
First very basic version of a split screen for message list + view
Add marker in message list for currently opened message
Add setting to configure the splitview mode
Add 1px divider between message list and message view in split view
Add hotkeys from MessageView to MessageList
Add message view menu items to MessageList
Go back to message list when using the back button in message view
Make sure swipe gestures only work on the message list
Fix "return to list after delete"
Get rid of MessageView activity
Fix back button behavior
Set MessageList title in action bar depending on display mode
Use theme-specific color for message list divider
Remove unused layouts
Extract string to strings.xml
Change default value of split-screen setting
Update help text for hotkeys
Fix handling of hotkeys to move to previous/next message
Add animation when switching from message list to message view