A custom button control. A original post found on reddit: https://www.reddit.com/r/Unity3D/comments/3bkpfh/anyone_here_an_expert_on_editor_extension/

CustomButton.cs

public static class CustomGUI {
    public static bool CustomButton(Rect position, GUIContent label, GUIStyle style) {
        bool wasClicked = false;

        int controlID = GUIUtility.GetControlID(FocusType.Passive);
        switch (Event.current.GetTypeForControl(controlID)) {
            case EventType.MouseDown:
                if (Event.current.button == 0 && position.Contains(Event.current.mousePosition)) {
                    GUIUtility.hotControl = controlID;
                    Event.current.Use();
                }
                break;
            case EventType.MouseDrag:
                if (GUIUtility.hotControl == controlID)
                    Event.current.Use();
                break;
            case EventType.MouseUp:
                if (GUIUtility.hotControl == controlID) {
                    GUIUtility.hotControl = 0;
                    if (Event.current.button == 0 && position.Contains(Event.current.mousePosition))
                        wasClicked = true;
                    Event.current.Use();
                }
                break;
            case EventType.KeyDown:
                if (Event.current.keyCode == KeyCode.Escape && GUIUtility.hotControl == controlID) {
                    GUIUtility.hotControl = 0;
                    Event.current.Use();
                }
                break;
            case EventType.Repaint:
                style.Draw(position, label, controlID);
                break;
        }

        return wasClicked;
    }

    // Default button style overload:
    public static bool CustomButton(Rect position, GUIContent label) {
        return CustomButton(position, label, GUI.skin.button);
    }

    // Layout overload:
    public static bool CustomButton(GUIContent label, GUIStyle style) {
        Rect position = GUILayoutUtility.GetRect(label, style);
        return CustomButton(position, label, style);
    }

    // Layout overload with default button style overload:
    public static bool CustomButton(GUIContent label) {
        return CustomButton(label, GUI.skin.button);
    }
}