Add execution and slot identity to runs

Stations that test several units at once can now record which fixture slot produced each run and which execution the runs belong to, so a batch is traceable as a whole and per slot.

• Added execution_id, slot_key and slot_name to the run API, returned on run get, list, header and metadata
• Added execution and slot filters to the run list, the timeline and the runs page, with the fields in CSV exports
• Added slot and execution details to the run overview, with a link to every run of the same execution