Management command to import latest EA measurement

Using ea-measurement-collector which is installed into api.libs.

Now you can add a station to the database then run:
```
python manage.py get_latest_ea_measurements
```

And the latest measurement will be fetched and inserted into the
database for each station.

https://www.pivotaltracker.com/story/show/75972824
[Delivers #75972824]
Add `run_every_10_minutes.sh` for Heroku scheduler

This will be run by heroku's scheduler addon. Updated README to document
how to install said addon.