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 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
