Project file management: Allow ability to organize project files

[alex-ketch]

To enable users to share their projects in an understandable way, fix errors, and clean up leftover artifact files, we'd like to have the ability to manage project files.
This includes operations such as renaming, moving, deleting, and re-uploading/overwriting files and directories.

Things to evaluate:

• Maintaining relationships between moved/renamed files and their original Sources
• How to handle deletions of files created from linked Sources (e.g. delete single file after pulling entire GitHub repository)

Related issues:

• Add ability to delete entire directories/folders #950