gcr: Allow using GBytes with GcrParser

This also solves a corner case where GcrParser would keep around a
pointer to the data passed into gcr_parser_parse_data(), even after
that data had been freed.

gcr_parser_parse_data() now copies the data passed in, where as
the new gcr_parser_parse_bytes() simply keeps a reference to the
GBytes.

https://bugzilla.gnome.org/show_bug.cgi?id=708736