add: distinction in results-db between run timestamp & data timestamp

[kenfar]

Right now the results database only knows when a check was run - not what time period the check was run against.

Add another set of timestamps for the start & stop time the check was run against. This is particularly important when incremental testing is being performed.

defines when process ran:

• run_start_timestamp
• run_stop_timestamp

defines period being checked:

• if mode == 'full', then it's all data, up to the runtime, more or less
  • because they could have data for the future in the table
  • or because maybe there's no data for the past 3 weeks in the table
• if mode == 'incremental', then it's the partitioning date used by the incremental checks
  • but there's a lot of different incremental date formats
  • maybe the setup should also provide a start & stop regular timestamp when it provides incremental checks?
• data_start_timestamp
• data_stop_timestamp

[kenfar]

Added in 0.1.5