Bug 7143: Release team 3.20

Bug 7143: Release team 3.20

Updated the release team with the roles for 3.20 pages on the wiki and
checked with the votes on the IRC meeting log.
Simplified the section on Former release team members by moving that
information (in a compressed format) to the Developers section.
If someone had a role for multiple releases, I used constructs as 3.X.
Sorted the Additional thanks-section.

Signed-off-by: Justin <justinvos@live.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
2015-01-14: Amended. Replaced abbreviations like RM by Release Manager.
Replaced one occurrence of 3.x by 3.X (for Owen).

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>