Allow for multiple time periods in a config

[Georgea75]

Currently when running Elara from a config only one time-period is allowed. This means you can not run a series of benchmarks (Such as LinkCounters) that are built using different time periods. This can often be the case when sourcing benchmark data from different authorities.

It would be ideal to be able to override the time period for individual benchmarks and add the capability for Elara to aggregate the time periods to the time period set in an individual benchmark. For instance if the config contained two benchmarks, one at 15-minute bands, and one at hourly bands. Elara would calculate the link volumes at 15 minute intervals and then aggregated them into hours for the hourly benchmark.