first_run and last_run_version property of workflow

- add `first_run` and `last_run_version` property for `Workflow`
- remove hardcode check for `settings.json` in `Workflow.store_data()`
- calling `self.settings` in `Workflow.__init__()` causes code coverage [failed](https://github.com/deanishe/alfred-workflow/blob/master/workflow/workflow.py#L1017) because `alfred_env` somehow got reloaded again. So doing a little tricky thing to fix it.