Refactor: libcrmcommon: separate IPC code into multiple files
    
    A significant amount of new IPC code will be added soon, so avoid the file
    sizes becoming ridiculous.
    
    Before:
      210 include/crm/common/ipc_internal.h
     1846 lib/common/ipc.c
     2056 total
    
    After:
      215 include/crm/common/ipc_internal.h
      755 lib/common/ipc_client.c
      103 lib/common/ipc_common.c
      903 lib/common/ipc_server.c
      146 lib/common/messages.c
     2122 total
    
    Rename newly exposed symbols per current style guidelines.