Add an option in settings to manage autostart on/off

Stickies autostart is automatically set when installing Stickies.
This is done creating a shortcut in "global" Startup menu : C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp

Of course, autostart can be afterwards set off removing this shortcut, or set on again, recreating the shortcut.

It would be nevertheless better to
- use registry key in HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run (or HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run) to manage autostart rather than Startup menu
- add a new option in settings to set autostart on or off