Rename EventNames.in to EventInterfaces.in

EventNames.in isn't used to generated EventNames.h. It is used to generate
EventInterfaces.h. After this change, I'm going to introduce a new
EventNames.in to actually generate EventNames.h, so I want to free up the name.

I've also moved a bunch of generated files out of the root shared intermediate
directory into the webkit subdirectory. This change helps us not polute the
shared intermediate directory. In a future CL, we should rename this
subdirectory to "blink".

R=eseidel

Review URL: https://chromiumcodereview.appspot.com/21130002

git-svn-id: svn://svn.chromium.org/blink/trunk@155108 bbb929c8-8fbe-4397-9dbb-9b2b20218538