Manager: add GZip middleware

Add support for GZip-compressed streams. This becomes increasingly
important when Shaman support gets added, as the blend files typically
used in studios are uncompressed to support binary diffing.

cmd/flamenco-manager/main.go

@@ -156,6 +156,7 @@ func buildWebService(
 
 	// Ensure panics when serving a web request won't bring down the server.
 	e.Use(middleware.Recover())
+	e.Use(middleware.Gzip())
 
 	// Load the API definition and enable validation & authentication checks.
 	swagger, err := api.GetSwagger()