CSV: add horizontal scrolling for CSV files

[alejandromumo]

When previewing a CSV file that has many columns, some of the columns are clipped from the iFrame and the user can't preview the CSV without downloading it.

[edbennett]

Thanks for tracking this. In case it's useful, in the current Zenodo deployment this is due to line 238 of https://zenodo.org/static/dist/css/3526.0d9b3c8be998e2e93a52.css:

overflow-x:hidden

Disabling this line in the web inspector restores the scroll bars as expected.

(I can't obviously see where this is getting set—searching this repository for overflow-x returns no results.)