Synchronise wgExtensionCredits with AUTHORS.txt, sort alphabetically

Added:
* Alex Monk,
* James Forrester, and
* Moriel Schottlender.

Removed:
* Brion Vibber,
* Gabriel Wicke,
* Neil Kandalgaonkar, and
* Subramanya Sastry.

The removed individuals work was mostly on Parsoid and other code now hosted
in other more appropriate repositories.

Change-Id: Icc843634f89491b00c203996bda6f6d02aefc52d
Merge "Synchronise wgExtensionCredits with AUTHORS.txt, sort alphabetically"