Control buttons can be added to the window's header with `lv_win_add_btn(win, icon, btn_width)`. `icon` can be any image source, and `btn_width` is the width of the button.
The title and the buttons will be added in the order the functions are called. So adding a button, a text and two other buttons will result in a button on the left, a title, and 2 buttons on the right.
The width of the title is set to take all the remaining space on the header. In other words: it pushes to the right all the buttons that are added after the title.
`lv_win_get_header(win)` returns a pointer to the header, `lv_win_get_content(win)` returns a pointer to the content container to which the content of the window can be added.