collect_ga_data Updates

Makes two changes to `collect_ga_data`:

- Changes the default date of collection from yesterday to two days ago. Currently, we run the nightly update at 23:00 UTC, but GA takes up to 24 hours to get click data up. This means that clicks between 23:00 UTC and midnight may not be available in the API by the time we run the collection the next day. Instead, we should run the command at 0:30 UTC and have it collect from two days prior; this will ensure at least 24 hours between click time and collection time.
- Adds `today` as a valid date argument. This will let us add an extra cronjob to dev that runs collection for the current day every 15 minutes, which will make testing click collection on dev a bit faster.