Add rotation of API and frontend logs

This adds rotation of the platform (API) and frontend rails app logs.
To see this work in development, deploy the changes like so:
```
ansible-playbook -u <you> -i development dev_all.yml -t logrotate
```
Then, to manually test the logrotate command:
```
ssh you@webapp1
sudo logrotate -f /etc/logrotate.d/api_rails_logs
sudo logrotate -f /etc/logrotate.d/frontend_rails_logs
```
Then look in `/srv/www/api/var/log` and `/srv/www/frontend/log`.

Oh, right, ok.  In that case, there's a `rails_env` variable defined in the `api` role that I can use, instead.