Add file comments for each source module

Each file contains only the copyright info. It would be good to have a 1-5 lines at the top of each file, describing the module.

- [ ] `antidote_app `
- [ ] `antidote_error_monitor`
- [ ] `antidote_node_event_handler`
- [ ] `antidote_pb_process`
- [ ] `antidote_warning_monitor`
- [ ] `binary_utilities`
- [ ] `binary_utilities`
- [ ] `clocksi_downstream`
- [ ] `clocksi_materializer`
- [ ] `clocksi_readitem_server`
- [ ] `clocksi_vnode`
- [ ] `cure`
- [ ] `dc_meta_data_utilities`
- [ ] `dc_utilities`
- [ ] `inter_dc_manager`
- [ ] `inter_dc_query_response`
- [ ] `inter_dc_query_response_sup`
- [ ] `inter_dc_txn`
- [ ] `log_utilities`
- [ ] `logging_vnode`
- [ ] `materializer`
- [ ] `materializer_vnode`
- [ ] `zmq_utils`