Refactor: all: make public API headers compatible with C++

This breaks backward API compatibility by changing the first argument of
send_cluster_text() from int to enum crm_ais_msg_class, and by renaming some
struct members:

struct Old name New name

cib_api_operations_s delete remove
lrmd_rsc_info_s class standard
lrmd_s private lrmd_private
stonith_s private st_private