File-based versioning for dropdown version selection

[michellexliu]

When switching versions of a submission via the dropdown, "lock" it to the same file (if the file exists in the other submission), similar to how the file stays when switching versions with the arrow. Possibly add some way of indicating which submission versions contain the file

[damianhxy]

@michellexliu I believe this is the current functionality?

For reference: #1503
My code determines the submission versions containing the current file and the arrow buttons jump to the correct header_position.

[michellexliu]

Oh hmm good catch; I just checked and the selected file persists with the arrows. However, if you select a different file & select the new version with the dropdown (even if it has the same file available), the file gets switched to the default one.

I'll update the issue to reflect this.

[damianhxy]

Hmm, that was something I considered implementing. It shouldn't be too hard to lock it to the same file when switching, although the drop-down might not have space to indicate versions with the file.

Plan

1. Mark versions with file with an asterisk (*)
2. If clicking on a version with an asterisk, jump straight to the file
3. When switching between files, update the select list