CMake dependency handling broken

[jobrud]

When the library is built for boost asio usage (with -DCLI_UseBoostAsio=ON) Boost::System is added to public link interface. That means all applications or other libraries which get linked against cli obtain automatically those dependency. Adding Boost::System to the link interface should be correct but then the cli cmake package also should take care about that dependency with:

find_dependency(Boost REQUIRED COMPONENTS system)

Which was commented out in commit fab1d75.