tools (common/template): add 2 new filters: `timestamp_to_hour` and `delta_to_human`: `timestamp_to_hour` give the hour corresponding to a timestamp, it will be used to display calendar for this time window. `delta_to_human` convert a delta of 2 timestamp to human readable time using `tools.common.date_utils` corresponding function.

these certificates are used for demo purpose only. Those must be the same as in
backend_e2e (they are generated there)