Ishtar

Imports: add a current line in import model (refs #3975)

Imports: add a current line in import model (refs #3975)

Step by step import: present object to be created, updated, etc. (refs #3975)

Step by step: large improvments on step display (refs #3975)

Show modified, sheet access for existing items, link between created,
updated fields and associated column.

Manage progression step (refs #3975)

Step by step import - WIP - refs #3975

Fix migrations - refs #3975

Manage CSV edtion and line by line import (refs #3975)

Step by step import: pagination (refs #3975)

Step by step imports: general check of lines to filter only relevant lines (refs #3975)