refactor media module, change --env to --root

This commit moves the media scanner out of the db module and into
a new module, media. We also change the --env parameter to --root,
which takes a path to a directory where the default configuration
and the transcoded media cache will live.

groove/webserver/requests.py

@@ -9,7 +9,7 @@ def encode(args: List, uri: str) -> str:
     Encode a request and cryptographically sign it. This serves two purposes:
     First, it enables the handler that receives the request to verify that the
     request was meant for it, preventing various routing and relay-induced bugs.
-    Second, it ensures the request wasn't corrutped or tampered with during
+    Second, it ensures the request wasn't corrupted or tampered with during
     transmission.
 
     Args: