(refactor) Rename window methods to targetWindow(), listWindows(), and window().

[hastebrot]

Changes:

• Add all missing window finder methods to FxRobot.
• Rename pos() to targetPos().
• Rename target() to targetWindow() to emphasize that it is a window-related method.
• Rename listOrderedWindows() to listTargetWindows() to emphasize the relationship to targetWindow().
• Add window() variants with parameter Predicate<Window>, Stage, and Node.

Interface:

interface WindowFinder {
    Window targetWindow();
    void targetWindow(Window window);
    void targetWindow(Predicate<Window> predicate);

    List<Window> listWindows();
    List<Window> listTargetWindows();
    Window window(Predicate<Window> predicate);

    // Convenience methods:
    void targetWindow(int windowIndex);
    void targetWindow(String stageTitleRegex);
    void targetWindow(Pattern stageTitlePattern);
    void targetWindow(Scene scene);
    void targetWindow(Node node);

    Window window(int windowIndex);
    Window window(String stageTitleRegex);
    Window window(Pattern stageTitlePattern);
    Window window(Scene scene);
    Window window(Node node);
}