Don't leak track StringPairArray
Normalize files containing unit test code:

Source files are split to place all unit test code into translation
units ending in .test.cpp with no other business logic in the same file,
and in directories named "test".

A new target is added to the SConstruct, invoked by:
    scons count
This prints the total number of source code lines occupied by unit tests,
in rippled specific code and excluding library subtrees.
Add non-unity build targets:

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.
Refactor NodeStore:

Manager is changed to be a Meyer's singleton, with factories automatically
registering upon construction.
Levelize SHAMap:

The SHAMap class is refactored into a separate module where each translation
unit compiles separate without errors. Dependencies on higher level business
logic are removed. SHAMap now depends only on basics, crypto, nodestore,
and protocol:

* Inject NodeStore::Database& to SHAMap
* Move sync filter instances to app/ledger/
* Move shamap to its own module
* Move FullBelowCache to shamap/
* Move private code to shamap/impl/
* Refactor SHAMap treatment of missing node handler
* Inject and use Journal for logging in SHAMap