Fixed app.yaml

app.yaml now ready for deployment in google appengine
Errors in error output missing

- Depending on the kind of problem, error codes and messages
could show up in different parts of the returned Json in
the get_zencoder_job_status function.

- In order for this same function to be able to correctly
reload the application, it had to be placed in the MainPage
handler.
Cleaning comments

Removed useless comments.