[642] First pass at download/upload of inventory

Updated import to make sure columns align
Updated to validate input on when an existing dataset isn't found
Only works with inventory items, does not list full datasets
Changes to separate template for download/upload and read-only download.
Changes the edit page to show two separate tools.  The download tool is now a
read-only view of the current datasets and inventory items on DGUK.
The upload tool now provides a template that users should download (and a link to the guidance doc - not yet there) and then re-upload when modified.

Text changes and modified upload results.

Also remove the stying for inventory search results as we want to temporarily remove them from search (next commit hopefully) for the prototype.

Inventory items are not shown in search, they're explicitly excluded