Nicer "Checkout aborted" description

[BinaryMuse]

When a checkout is aborted because untracked changes would be overwritten, we get this notification:

It might be nice to clean this up a bit:

• Separate the final sentence onto its own line
• Put the list of files in a bulleted list (maybe? what about if there are a lot of them)

[simurai]

• Change to a "warning" (orange)? Error feels a bit strong.
• Have a "discard all changes" button? I often just test stuff that I don't intend to keep. Be able to easily discard in the notification would be handy.