Optional progress window

[DanielSWolf]

Currently, the most user-friendly progress output supported by Rhubarb Lip Sync is an ASCII art progress bar written to the console. That makes it hard for integrations into third-party applications to show a nice progress dialog.

Let's add a --progress-window option that shows a graphical dialog window in addition to the normal output. This dialog should have the following features:

• It shows a graphical progress indicator
• It allows the user to cancel processing
• It shows any info, warning, and error messages
• It optionally also shows debug and trace messages
• It allows the log output to be copied to the clipboard for issue reporting