Added file creation reverting and DB rollback on error.
Added error display on failed import.
Extracted likely shown import form/error text to translation files.
Moved export templates elements into their own folder for better
grouping of logical usage.
Within the base export template, added some body classes to allow easier
targeted customisation via custom head css.
Split content of export templates into smaller partials for easier
future customization.
Closes#3443