[uievents] "Legacy" appendices should be normative (#50)

Copied from W3C Bugzilla: https://www.w3.org/Bugs/Public/show_bug.cgi?id=28967

##### Ms2ger 2015-07-20 07:46:23 UTC
Browsers need to implement them, so there's no reason to make them informative.


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https://github.com/w3c/uievents/issues/50