also namespace the properties names when using the child strategy

@dbu @dantleech

if we want to change this .. now is the time I guess.
a migration script should not be too hard to write.

i think this makes it easier to write/generate search queries even when we deal with a mix of strategies. it does however mean that f.e. if we have a title property inside a translatable (using child strategy) and a non translatable document then we will not find both anymore if we search for "title". this can be considered a plus or a minus ..