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.

You'll find install instructions in documentation (see doc/installation.rst).

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