Connecting folder displays alarming "Upload" warning message

[JulienVig]

The webapp allows connecting files in two different modes:

• connecting files by label, with one drag and drop zone for each task label
• connecting a csv linking filenames to labels and then all files at once:

When using the 2nd option, the user is allowed to select the folder containing all the files (rather than selecting the files themselves). Selecting a folder currently poses two problems:

1. The selection menu displays an "Upload button" (at least on Mac OS) while we would prefer something like "Select" or "Connect" as there is no upload happening
   
   
2. Selecting a folder with many files displays a warning message on Firefox and Chrome (not on Safari) asking the user to confirm whether they actually want to upload that many files.

Additionally, there is a behavior inconsistency, users can select a folder with the button (and not files) but can only drag and drop files which many confuse users. I tried to allow drag and dropping anything and detecting the nature of it but didn't manage to do it quickly.

• [ ] Allow users to connect a folder without anything displaying the word "Upload"
• [ ] Allow users to connect a folder without warning
• [ ] Allow users to drag and drop a folder