Enable VisualEditor by default on Wikimania 2014 wiki

Change-Id: Ie0dda60e0c38c0e2ffa315c79abf5edaae29c1d5
Follow-up 73ab798a: Also enable MediaWiki.org's Skin namespace in VisualEditor

Change-Id: I783a80cc836ac89e7978ee1b838b6fce1427f039
Remove whitelist entry for now-graduated MediaViewer BetaFeature

Change-Id: Id77bf845f7bbf52ff18237543348104fcfb81ef2
Remove references to the Math VisualEditor BetaFeature (now graduated)

$wmgMathVisualEditorDefault hasn't been used in production for a few months
now.

Change-Id: I84488427270f87b1ce6ae4f79a1ab40618e598c7
Merge "Remove references to the Math VisualEditor BetaFeature (now graduated)"
Merge "Remove whitelist entry for now-graduated MediaViewer BetaFeature"
Merge "Follow-up 73ab798a: Also enable MediaWiki.org's Skin namespace in VisualEditor"
Merge "Enable VisualEditor by default on Wikimania 2014 wiki"