#761 Various suggestions

[Snuff Daddy]

• Send Feedback option on the Help menu.
• The "Command Line Options" tool creates its popup window partially off the screen, at least on a 4K monitor.
• Need stock hotkey for Stop, other than the media stop key.
• The Window Class should be "SMPlayer" not "Qt5QWindowIcon", so that another application such as DJ Jukebox can find it and send it keystrokes. Only the main window should use this class.
• Hotkeys stop working sometimes. Focus problem?
• Open File should allow you to select multiple files.
• Hotkeys generated by the keybd_event() API are ignored.