Support for folders in Briefer.

# Context

So, for some context for this feature request:

I'm a university student in a research project related to Multi-modal saliency models. In this case, we need to analyze data and compare from two sets of data: one where users heard audio and the other where the users didn't hear the audio. Now, the thing is that the two types of data are differentiated by folders, not filenames.

Right now, on the cloud version of briefer, I can only add single files. However, since the data is differentiated by folders, such as "without_sound/_band/user1.csv" and "with_sound/_band/user1.csv", there will be multiple files with the same name, but different data.

Some examples here to demonstrate what i'm talking about:

# Feature Request

So, the feature I'm requesting is to add support for folder navigation in briefer, such as adding and removing folders to allow for files with different datasets to be added without the confusion of knowing which one is which, or atleast some sort of grouping for files would be nice.

Also, sorry for the grammar here, English is not my native language and writing about a field I'm not familiar with is kind of hard.

No source files, tests, or entry points are named in the issue. Start by locating the cloud file-upload and navigation entry points, then trace how uploaded files are listed and identified. Done means users can add, remove, navigate, and distinguish files organized in folders or an equivalent grouping.

Written by the indexing model from the issue text.