…eferences in guides to explore tools [ref #6919]

…on btn to Style Guide [ref #6919]

The rule is "The eyeball is present if the Preview tab is present."

There are edge cases to consider around guestbook, terms of use,
restricted data, etc.

For now we at least check if the appropriate tools are in place.

Our goal is to include file-download-popup-fragment.xhtml onto another
location, the Preview tab on the file page, while still displaying
it as a popup on that page.

In the Preview tab the input fields weren't showing up and we discovered
that commenting out "binding" made them appear. Commenting out "binding"
resulted in validation not working. Additionally removing process=@this
along with much more refactoring, got validation working. Bean validation
was added as well.

The hope is that with this commit in place, we can switch back to trying
to get the extra "include" (mentioned above) working.

Some things to note about this commit:

- Custom UIInput fields have been removed in favor of standard
Bean Validation.
- The GuestbookResponse field was removed from FileDownloadHelper because
it was confusing to sometimes set it and other times pass it in as argument
to various methods. Now we always pass it in.
- Various unused code was deleted.
- process=@this wasn't removed from the "package" code and it's unknown
if that code is working.

Conflicts:
src/main/java/ValidationMessages.properties

This commit does two things:

- Include file-download-popup-fragment.xhtml (where guestbook and terms live) on the Preview tab.
- Allow files to be previewed in more scenarios, such as when datasets have a guestbook or terms.

There are a couple TODO/FIXME items not addressed:

- <p:focus context="downloadPopup"/> was commented out.
- @Form is used in a place where it could be more precise.

…ic to btn txt on file pg [ref #6919]

…ref #6919]

Without this update, the failure case was this:

1. When there are required fields, click Accept without filling them in.
2. Fill in all required fields and click Accept.
3. The form remains and you cannot see the preview.

Conflicts:
src/main/java/ValidationMessages.properties

Lots of edits were made previously in this branch.

We've switched to Bean Validation, which is done centrally instead of
being only in the UI.