Regression was introduced in 3372dfcd3e.
Only when platform-specific code can give us the global time of the
last user input event we rely on idle time for notifications hiding.
Fixes#5791.
Also implement panels that appear in all spaces on macOS.
Using them for calls panels and custom notifications, so it
will be possible to use custom notifications in macOS as well.
Don't deactivate the application when the main window is hidden.
Such behavior provides some unwanted windows reordering in the
current workspace when the window is hidden by Cmd+W.
Ignore app activation by applicationDidBecomeActive: notification
for a short period of time after a user notification for other app
instance was received (the system sends them sometimes and the main
window is shown + activated for a wrong instance of the application).
