Metrics indexing efficiency

[hopshackle]

MetricsGameListener.eventToIndexingColumn() now applies Tick as the indexing column for Turn or Tick based metrics, but Round for Round ones.
This was recently fixed from using Turn as the indexing column for Turn metrics - this caused a problem because Turn numbers are not unique as we may have Round 1 Turn 2, Round 2 Turn 2, Round 3 Turn 2 and so on. If Turn is used as the indexing column the result is that only the data from the last Round is recorded. (Hence the fix to use the safely unique Tick for indexing...this has no impact on the final result).

A possibility this raises is that this method could be removed, and we could always index on Tick.