Fixed MediaScan Issue w/ Directories

MediaScan wasn't being done recursively, so moving a directory which
had content to a different location wouldn't include the children
in the scan. This implementation makes sure all files and folders
within the directory are also scanned.  Tested against a dataset of
1000 videos, so performance seems fine.

Change-Id: If3c94f92d96d2d78bb0664112ea235f3e3669363
Ticket: QRDL-1009