Add the "Add a statement" form at the right place

## User story

As fact checker on a page with lots of previous statements, I can see the "add a statement" form on its correct timecode instead of the beginning of the page so that I don't see the whole list of statements scrolling when I submit the form.


## Best solution for this problem

When clicking on "add a statement", insert the creation form at the correct timecode (Where the current scroll is likely to be)

Start from the page's "add a statement" interaction and observe how the creation form is placed when the page contains many previous statements. The work is done when clicking "add a statement" inserts the form at the current scroll's timecode rather than at the beginning of the page.

Written by the indexing model from the issue text.