Run submission in a separate thread, and more explicit state

Also more explicit timeouts and an overall better handling of errors.

benchmark/submission/timeouts.py

@@ -0,0 +1,14 @@
+"""Timeouts for HTTP traffic, all in seconds."""
+
+submit = 30
+verify = 10
+
+# This one is tricky, as the user may need to take the time to register a new
+# Blender ID (which includes confirmation of their email address). We should
+# not show too scary messages when it comes to timeout errors when waiting for
+# a token, and just expect it to time out when a new Blender ID account is
+# registered.
+#
+# It should be long enough for a normal flow, though, as after this timeout
+# the temp HTTP server on localhost:$RANDOM is down again.
+wait_for_token = 15