Move admire types into dedicated 'admire_types' CMake target

This makes it much simpler to share type definitions between the library
and the daemons.

- C++ types are now declared in admire_types.hpp
- C & C++ types are defined in types.cpp. The reason for them being in
  the same file is that the C type-creation functions use logging
  facilities that are C++ code. Until we offer a C interface for them,
  C-type functions need to be compiled with a C++ compiler.