Fix scan media issues

There are two issues with the "Scan Media" task

1. Scanning a Directory doesn't discover new media files in the directory
2. Scanning a file takes too long (about 1 second per file).  This is a problem when looping over many files.

Suggested fix options:

1. Option to scan files asynchronously.  We don't need any output from the scan action to proceed
2. Speed up synchronous file scan
3. Fixing the directory scan to pick up new files inside as new media (e.g. by Google Photos)