Small WG/IC/IG content updates

• https://www.eclipse.org/membership/exploreMembership.php: please update the orange button in the header to "Explore our Industry Collaborations"
• https://www.eclipse.org/europe/ and https://www.eclipse.org/membership/exploreMembership.php: please update the orange button in the header to "Industry Collaborations"
• https://www.eclipse.org/membership/: please make these changes
• https://www.eclipse.org/org/workinggroups/explore.php#interest-groups: please update the grey button to say "Not an Eclipse Member?" and update the orange button to say "Eclipse Member ready to join now"and link to https://www.eclipse.org/collaborations/interest-groups/contact/
• https://www.eclipse.org/collaborations/: add a third button to the header "Explore Collaborations" that links to https://www.eclipse.org/org/workinggroups/explore.php

/cc @sgiacomoni2as