bluehats/bluehats-semester-of-code.md: Remove year

The internship program will really take place in 2022 for the first
year, even though it has been launched in 2021.
bluehats/ateliers.md: Add link
contacts/index.md: Announce office hours
contacts/index.md: Add link to get in touch with BlueHats
bluehats/index.md: Add link to where meet BlueHats
a-propos/index.md: Add embedded presentation
a-propos/index.md: Link to a wiki page
Remove job announcement
gazette/index.md: Fix error
utiliser/marches-....md: Add link to csv
utiliser/marches-....md: Fix wording
utiliser/marches-....md: Fix links
utiliser/marches...md: Add contact information
Add information on "marchés support et expertise logiciels libres"
bluehats/ateliers.md: Small fixes
bluehats/ateliers.md: Add link to presentations
bluehats/ateliers.md: Add workshop
bluehats/ateliers.md: Add link to the replay of today's workshop
bluehats/bluehats-semester-of-code.md: Add link to the list of ideas
bluehats/ateliers.md: Remove link to a session

The video for the SambaÉdu session was not the right one.