WG to IG

AICE is moving to an Interest Group. Website has to be updated:

• Smart search and replace WG occurrences by IG (in title and paragraphs).
• Remove Participation Agreement and Charter
• Replace by a sentence saying "Moving to an IG, Contact FZ and GB"
• Remove Monthly meetings
• Add link to IG description: https://www.eclipse.org/collaborations/interest-groups/

/ping @gblondelle @scorbett