Import CSV files of any size, with a progress bar

The importer used to stop at 5,000 rows. It now takes a file of any size. The preview and the import both run in batches, with a progress bar showing how many rows are done and roughly how long is left.

• Very large files are slowed down a little so the CRM stays fast for everyone, and the import carries on by itself. A dropped connection is retried when doing so can't create duplicates.
• Stop import keeps every row imported so far. If an import stops early, it tells you which rows went in and how to finish.
• The preview spots duplicate rows anywhere in the file, not only near each other.

Cells with several values

When a column has lists in its cells, like vip, newsletter, the mapping step now explains what will happen. For a Tags or Multi-select field, it shows how one cell splits into separate values and which values are new. It also warns when rows will be skipped because a multi-select field doesn't offer one of their values. For a single-choice dropdown, it says the whole cell will be one value. It also flags |-separated lists, which aren't split.