An alternative to the unity build, the classic build compiles each
translation unit individually. This adds more modules to the classic build:
* Remove unity header app.h
* Add missing includes as needed
* Remove obsolete NodeStore backend code
* Add app/, core/, crypto/, json/, net/, overlay/, peerfinder/ to classic build
The SConstruct is modified to provide a new family of targets, ending with
the suffix ".nounity", which compile individual translation units instead of
some of the unity translation units ("classic" builds). Two modules updated
for this treatment are ripple/basics/ and ripple/protocol/, with plans to
update more in the future. A consequence is longer build times in some cases.
A benefit of classic builds is that missing includes can be identified
through compiler errors.
