Web file management, upload

[SpComb]

Implement a HTTP /vfs API with the following endpoints:

• GET /vfs
• GET /vfs/<mount>
• GET /vfs/<mount>/<directory>/
• GET /vfs/<mount>/<file>
• POST /vfs/<mount>/<directory>/
• PUT /vfs/<mount>/<file>
• DELETE /vfs/<mount>/<directory>/
• DELETE /vfs/<mount>/<file>

File uploads with a Last-Modified request header also set the filesystem mtime to the original file mtime.

Use a new vfs_dev to return vfs stat (sectors total/used/free) for operations.

Add a new Files view to the Vue web UI:

• List of mounts with their filesystem usage and free space (updates on upload/delete)
• List of directories, expandable
• List of files, with size/mtime metadata
• Create new directories
• Upload new files, with file upload progress
• Download files
• Delete files
• Delete directories