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.

sat/tools/common/template.py

@@ -22,9 +22,10 @@ import os.path
 import time
 import re
 import json
+from datetime import datetime
 from pathlib import Path
 from collections import namedtuple
-from typing import Optional, List, Tuple
+from typing import Optional, List, Tuple, Union
 from xml.sax.saxutils import quoteattr
 from babel import support
 from babel import Locale
@@ -467,6 +468,8 @@ class Renderer(object):
         self.env.filters["next_gidx"] = self._next_gidx
         self.env.filters["cur_gidx"] = self._cur_gidx
         self.env.filters["date_fmt"] = self._date_fmt
+        self.env.filters["timestamp_to_hour"] = self._timestamp_to_hour
+        self.env.filters["delta_to_human"] = date_utils.delta2human
         self.env.filters["xmlui_class"] = self._xmlui_class
         self.env.filters["attr_escape"] = self.attr_escape
         self.env.filters["item_filter"] = self._item_filter
@@ -773,6 +776,7 @@ class Renderer(object):
     ) -> str:
         if is_undefined(fmt):
             fmt = "short"
+
         try:
             return date_utils.date_fmt(
                 timestamp, fmt, date_only, auto_limit, auto_old_fmt,
@@ -781,7 +785,12 @@ class Renderer(object):
             )
         except Exception as e:
             log.warning(_("Can't parse date: {msg}").format(msg=e))
-            return timestamp
+            return str(timestamp)
+
+    def _timestamp_to_hour(self, timestamp: float) -> int:
+        """Get hour of day corresponding to a timestamp"""
+        dt = datetime.fromtimestamp(timestamp)
+        return dt.hour
 
     def attr_escape(self, text):
         """escape a text to a value usable as an attribute