FEATURE: Download search/xref exports in CSV format

[tillprochaska]

Is your feature request related to a problem? Please describe.
Aleph provides options to export search results and xref matches. Right now, Aleph supports export in Excel format only. (Large) Excel files can be difficult to work with, to the point where even converting a huge Excel file to e.g. CSV can be difficult.

Describe the solution you'd like
It would be nice if users had the option to choose CSV as an alternative format for exports, as CSV files can be processed much more efficiently.

Describe alternatives you've considered
-/-

Additional context

• Based on user feedback.
• FollowTheMoney already has built-in support for exporting entities to multiple formats, including Excel and CSV. In order to add support for CSV exports to Aleph, it might be enough to conditionally swap out the concrete exporter class.