Bug 838598 - Part 1: Rename nsHTMLMenuItemElement to HTMLMenuItemElement. r=Ms2ger, r=janv

--HG--
rename : content/html/content/src/nsHTMLMenuItemElement.cpp => content/html/content/src/HTMLMenuItemElement.cpp
rename : content/html/content/src/nsHTMLMenuItemElement.h => content/html/content/src/HTMLMenuItemElement.h
Bug 838598 - Part 2: Convert HTMLMenuItemElement to WebIDL. r=Ms2ger, r=janv