Prompt user to skip or redownload existing files #132
Description
What
When the user selects a set of files to be downloaded, check the default output directory or the user specificied output directory, check which of the requested files already exist, then ask the user whether they want to skip the existing files or redownload them.
Why
Skipping over the existing files can significantly reduce time and the user won't have to redownload existing files. Also, the download fails halfway through sometimes (or other events, e.g. laptop dying, can cause the download to stop) and this would allow the user to continue on with the failed download.
How
Add a question in the interactive CLI to check for existing files and ask the user to skip/redownload existing files. In the case of direct inputs, we need to think a little bit more about how or if we want to implement this feature. This is because we want the direct input to be able to run without requiring further interaction from the user (such as when you're running Makefile or Justfile commands).
Deliverables
Modified main_cli.py functions to add the new features described above.