Implement KvpFrame in C++ using std::vector

KvpFrame was implemented using GList. Given the current desire
to distance ourselves from glib and acquaint the project with
C++, the standard library thereof, and boost libraries, KvpFrame
has been replaced by an implementation that uses a std::map<
const char *, KvpValueImpl *>.

There were some cases of the KvpFrame's glist being accessed
directly. A new API to help callers access the KvpFrame's contents
systematically by providing a list of keys has been created, and
call sites of the GList code have been updated.

Another deprecated #define was found and removed (kvp_frame_set_str).