AUTHORS.txt: Re-update for late 2014

Add Marielle to principal authors (previously missing).

Add Andrew Garrett, Brad Jorsh, Dan Duvall, Derk-Jan Hartman, Frederico Leva,
Jon Robson, Kaity Hammerstein, Kunal Mehta, Niklas Laxström, Quim Gil, Sam
Reed, Sam Smith, Vikas S Yaligar, & addshore, Helder and Jiabao to the patch
contributors list, based on git shortlog perusal. Moved Neil Kandalgaonkar to
the VisualEditor-core list only.

Change-Id: Ieef11abf208216f22a95cb85cbc8ce54a7f30501
Merge "AUTHORS.txt: Re-update for late 2014"