Added IDS-related presentation at IUGG (July 2023)

Added a picture of the DORIS equipment at Hanga Roa in the Sitelogs pages and in the Gallery

Added IDS presentations at IERS Directing Board meeting (2020, 2021, 2023) and GGOS Bureau for Networks and Observations meeting (July 2023)

Added an illustration of the constellation of satellites carrying DORIS 

Updated version of the timeline of the satellites carrying DORIS

Updated version of the plots showing data availability and number of satellites