Switch to new schedule endpoint

[tomaspalma]

Sigarra has a new schedule endpoint that is easier and less buggy to construct than the current implementation.

As for now, the defined steps that appear to be needed to have this work are:

1. Get the endpoint from the html of the user
2. Store that endpoint in the session of the user
3. Change the methdod that converts sigarra schedule to tts schedule as the response format sigarra has changed