ContentHandler implementations were not including fields
defined by their parent ContentHandler classes.
merge method is added to the SearchIndexFieldDefinition
mock in SearchEngineTest, to allow merges of fields
in the way that SearchIndexFieldDefition implementation does.
Change-Id: Id04a51528f566da2666bad0394a2f61c949c69b4
* All content handlers that deal with code/data tend to have
English as their page language & pageview language, so moved common
code to the abstract CodeContentHandler class.
* Renamed JSONContent & JSONContentHandler into JsonContent*
Change-Id: I46819a0572ef5becc211d0d82471ff7102edaa3c
