companion: get/set timezone offset for clock

* Add tz_offset companion prefs and get/set commands for companion cli
* Use tz_offset for clock on display

Signed-off-by: Aleksei Mamlin <mamlinav@gmail.com>

examples/companion_radio/MyMesh.cpp

@@ -2166,6 +2166,22 @@ bool MyMesh::handleCommand(const char* command, uint32_t sender_timestamp, char*
     return true;
   }
 
+  if (strcmp(command, "get tz.offset") == 0) {
+    sprintf(reply, "> %d", _prefs.tz_offset);
+    return true;
+  }
+  if (memcmp(command, "set tz.offset ", 14) == 0) {
+    int8_t tz = atof(&command[14]);
+    if (tz < -12 || tz > 14) {
+      strcpy(reply, "Error, must be from -12 to +14");
+    } else {
+      _prefs.tz_offset = tz;
+      savePrefs();
+      strcpy(reply, "OK");
+    }
+    return true;
+  }
+
   return false;  // not handled
 }