[ticket/11122] Add EXreaction to docs/AUTHORS.

PHPBB3-11122
[ticket/11122] Move rxu to 'Former Contributors' section.

PHPBB3-11122
Merge remote-tracking branch 'github-bantu/ticket/11122' into develop-olympus

* github-bantu/ticket/11122:
  [ticket/11122] Move rxu to 'Former Contributors' section.
  [ticket/11122] Add EXreaction to docs/AUTHORS.