lokimq.cpp and lokimq.h were getting monolithic; this splits lokimq.cpp
into multiple smaller cpp files by logical purpose for better parallel
compilation ability. It also splits up the lokimq.h header slightly by
moving the ConnectionID and Message types into their own headers.
Depend on cppzmq-static when doing a static build.
cppzmq-static itself has a dependency problem with libsodium, so
explicitly set the missing but required libsodium dependency on it.
- Properly export the lokimq::lokimq target for use as a sub-project
- Drop the lokimq::static target; the library will just be static or
non-static dependending on cmake's BUILD_SHARED_LIBS setting
- Properly disable cppzmq tests (the previous setting resulted in cmake
warnings)