deposit: non spaghetti code of the modal_preview

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
deposit: templates rendering with Hogan

* Uses Hogan to render the template of the table that populates the
  modal window to display the data that is about to be imported.

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
Co-authored-by: Kamil Neczaj <kamil.neczaj@cern.ch>