Video info scanner fix: scan the entire subtree of path passed to scanner.

This fixes JSON-RPC's VideoLibrary.Scan and UpdateLibrary builtin not picking up changes when called with a path as parameter and changes are not visible directly in this directory. It now does the same as the global update function: queuing all known directories and sub-directories for scanning.

Also fixes hashing never getting used when using the 'Scan for new content' function in GUI.