Allow disambiguate and id header arguments on web

Currently these do not affect the article's ID as there is a fundamental limitation of the convert function, which determines the "file path" based solely on the title content, and ignores the title arguments such as disambiguate. The ID of the first header, the toplevel ID, then just gets fixed to that (as is meant to happen, first toplevel gets Id fixed), ignoring disambiguate.

This is worked around on web upload by passing the id as the path explicitly as an argument. But this argument is not available on web UI, and it would be ugly anyways, what we want is for it to "just work" by default without the user having to explicitly set an ID on web UI.