Provide more information about run/job timing

Progress so far:

Jobs
- [x] `Job.updated` column added (with test)
- [x] Alembic migration added for `Job.updated`
- [x] `Job.timestamp` should be renamed to `Job.posted`
- [x] Alembic migration added for `Job.timestamp`

Runs
- [x] `Run.scheduled` property added (with test)
- [x] `Run.updated` property added (with test)
- [x] `Run.timestamp` should be renamed to `Run.posted`
- [x] Alembic migration added for `Run.timestamp`