Add ability to minimize to taskbar

[airbornelamb]

Under Windows 7+ when SynNotes is minimized it goes to the tray. There should be a setting to adjust whether or not this happens. Most programs minimize to the taskbar.

[sergeevabc]

@sepich, tray/taskbar behaviour needs to be improved, indeed.
I do not like the flickering that occurs when app is invoked as icon disappears from tray, let it stay there.