Documentation for new editable_text tag

I've added documentation for the new editable text tag and documented the deprecation of editable_short_text and editable_long_text. Here's what I changed:
- Added a page for the new editable_text tag.
- Moved documentation for the deprecated editable_long_text and editable_short_text tags to a sub-section of the editable_text page.
- Set the editable_short_text and editable_long_text pages to redirect to editable_text. I also emptied their contents and removed them from the side menu.