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).
Now each platform-dependent module declares its interface in
platform/platform_module.h file and after that includes platform-
specific headers like platform/win/module_win.h with implementation.
Also removed the legacy WinRT platform-dependent implementations.
A regression was introduced in 1.0.12 version which led to wrong
activations of the main window: if a custom popup menu was shown
for the tray icon or a custom notification was clicked.
