update zh_cn translation.

Use JavaScript localeCompare to sort "Name" field in dataTable.

Display username in ImpersonateForm.

Raise form ValidationError when importing non-importable csv data

raise form ValidationError when importing csv with columns containing non-ASCII characters while the csv is not utf-8 encoded.

Sandbox: Store the page_data in the session along with the answer_data.

Otherwise, the answer_data could be inconsistent with the page_data.
For instance, when sandboxing a choice question that is shuffled, the
answer_data is matched with a particular permutation which is part of
the page_data.

This reverts commit 2e147638.

number of points.