message: use pkg-config in FindJsonCpp for Ubuntu
diff: -find_package(jsoncpp CONFIG)
  +find_package(jsoncpp CONFIG QUIET)
  +
  if(JsonCpp_FOUND)
  message(STATUS "Found jsoncpp via config file: ${JsonCpp_DIR}")
  if(NOT JsonCpp_LIBRARY)
  @@ -9,10 +10,19 @@ if(JsonCpp_FOUND)
  endif()
  endif()
  else()
  - find_path(JsonCpp_INCLUDE_DIR NAMES json/json.h)
  - find_library(JsonCpp_LIBRARY jsoncpp)
  + find_package(PkgConfig)
  + pkg_check_modules(PC_JSONCPP jsoncpp)
  +
  + find_path(JsonCpp_INCLUDE_DIR
  + NAMES json/json.h
  + HINTS ${PC_JSONCPP_INCLUDEDIR} ${PC_JSONCPP_INCLUDE_DIRS})
  + find_library(JsonCpp_LIBRARY
  + NAMES jsoncpp
  + HINTS ${PC_JSONCPP_LIBDIR} ${PC_JSONCPP_LIBRARY_DIRS})
  +
  include(FindPackageHandleStandardArgs)
  find_package_handle_standard_args(JsonCpp DEFAULT_MSG JsonCpp_LIBRARY JsonCpp_INCLUDE_DIR)
  +
  mark_as_advanced(JsonCpp_INCLUDE_DIR JsonCpp_LIBRARY)
  endif()
  