Simplify bulk content upload

[mikedawson]

Is your feature request related to a problem? Please describe.
Admins / teachers want to be able to upload content in bulk (e.g. an entire folder, selecting multiple files, etc)

Describe the solution you'd like
Drag/drop a file or folder on a computer onto the library or courses to add content in bulk. When more than one file is added, a bulk content import should allow the user to select how files are named (e.g. use file names or use supported metadata), sort order, etc.

Describe alternatives you've considered
Can import from links (Apache) - but this is not user friendly.

Additional context
Need to consider how subfolders will be handled when added to a course. Submodules are currently not supported.
Need to consider how to handle unsupported files in folders (possibly upload the binary and allow the user to download/open in an external app).