ChangeJson has grow in size and became very hard to read. This commit is
a first step at modularizing the logic by factoring out RevisionJson.
It makes the concept of lazyloading purely internal to
{Change,Revision}Json by removing the parameter and deriving the
parameter based on the provided options only.
Change-Id: Ie04ec27723d145518277c84970462ab0e6c01979
ed56ba1370