Nah - deleted `Window::pollEvent`
Added `WindowEventsPoller` header with `WindowEventsPoller` and:
  - `registerWindow` method
  - `PollEvents` abstract  method
uses `map<id, window>` as container_type
Added `WindowEventsPoller` source file with `WindowEventPoller::registerWindow` method definition
Shh... small letter...
shh...