Resolve TSV download issues

[justincorrigible]

As part of the implementation we've encountered a bug in which pressing any of the two default tsv download options causes a critical error in the API.

Upon further inspection, turns out the issue is Arranger was customised for a cancer-file-centric model, which included specific fields that caused errors when missing.

This ticket adds code guards and updates the UI to use the improved arranger version.

---

bonus: As per conversation with @joneubank, we're adding a default "max rows" value for these, as large numbers may overwhelm the servers and potentially enable unintentional DDoS by insistent users.