Parsoid/Todo:Sanitizer

Tracked in Bug 39179

Sanitizer

 * Check whether there is adequate test coverage in parserTests.txt and/or other php sanitizer tests.
 * If not, add additional tests to parserTests.txt
 * Go through ext.core.Sanitizer.js and look at FIXMEs -- there are a couple that merit attention.
 * Understand what the correct behavior is when the same attribute is defined multiple times. Parsoid duplicates PHP parser behavior.  So, both PHP sanitizer and Parsoid might need fixing.
 * Ex: foo
 * In Firefox, foo is display in blue and bold (the first occurrence of style). But, the PHP parser hides foo (the second occurrence of style).  What is the correct behavior?