Update html fixtures for layout tests

[jams2]

Adds pytest as a dev dependency, and updates the html layout fixtures to match the html being rendered by the package.

Summary of changes:

• "hint" elements changed from div to span
• move "hint" elements below error messages where appropriate
• added missing class names, e.g. "tbxforms-input--text"
• add missing error summary elements
• add various attributes to date inputs