json serialization for rpc-relevant monero types

Structured {de-,}serialization methods for (many new) types
which are used for requests or responses in the RPC.

New types include RPC requests and responses, and structs which compose
types within those.

# Conflicts:
#	src/cryptonote_core/blockchain.cpp

CMakeLists.txt

@@ -689,6 +689,8 @@ endif()
 
 include(version.cmake)
 
+find_library(ZMQ_LIB zmq)
+
 function (treat_warnings_as_errors dirs)
   foreach(dir ${ARGV})
     set_property(DIRECTORY ${dir}