Adding form element to output

Poppler takes care of almost everything, I simply added the form tags at the end of every page.
Almost all the styles are managed by `StateManager`, so we can use the class names, in order to make the output file smaller. You can read some other parts for reference.
Not sure if we need a special class name for form elements, which are defined in `src/css_class_names.cmakelists.txt`.

Do we need the `id` for the elements, maybe we need to extract the information from JavaScript, but not sure if there are other ways.