Populate fact check notes and activity modal fix

www.agileplannerapp.com/boards/173808/cards/5999

##### Populate fact check notes
Rails' `textarea` view helper doesn't work with blocks, hence replacing with [`<textarea>` element](https://github.com/alphagov/publisher/commit/00bce1dfa04b6c789953e74af7e895be61dbd58d#diff-7a9a32930bceafecfbf0a92d3b68e36dR19).

##### Activity modal not appearing on tabs other than '#edit'
The edition form contains edition activity fields which are rendered in a modal when an editor clicks a button to perform an activity e.g. clicks "2nd pair of eyes".

Earlier when the form was rendered within the first `tab-pane`, switching to another `tab-pane` caused these edition activity fields to have style `display: none`. as a result, clicking on an activity button didn't bring up a modal, and just showed an overlay.

Now, the edition form wraps the `tab-pane`, and the edition activity fields are moved outside the `tab-pane`. Moving across modals doesn't affect the style of these activity fields, and so a modal appears when performing an activity from any tab.

I've chosen to render all forms using the helper `semantic_bootstrap_nested_form_for` because it is just a wrapper over `semantic_form_for`, which adds additional behaviour like `link_to_remove` for nested attributes.

Removed unused helper method `produce_fact_check_request_text`, and unused `.no-auto-save` on smart answers form.