Fix #341 PluginConnector

The internal notification std::map could cause notifications in non-deterministic order due to internal ordering by plugin pointer which can vary from rank to rank.

The old naming "frequency" was corrected to "period" internally. Interfaces have still to be renamed.

run time tests:
 - [ ] default KHI (16 GPUs)
 - [ ] rebased phase space branch (16 GPUs)