There's a new class Module to organize modules in the application. Prevents
errors from cyclic require's.
The number of modules can still be reduced by organizing them better.
Also removed some methods/routes that were not being used and will have to
be refactored anyway if they are needed in the future. They are: get_join,
to join the session getting the username and password from the url, and
post_upload, to upload presentations from the html5 client (this was a
specially big method).
Now there's a 'config' module to store global configurations.
The requires have to be made locally for the modules needed, can't just
require everything on app.js as it was before.
