Logging, Easier Starting

A couple changes:

* ecrn_app now has a start function, so you can just add ```-s ecrn_app``` to an erl command to get erlcron to start
* Added logging with lager when a cron job runs. This makes it easier to see what's happening, and you don't have to have the same log line in every cron job you run. Since it's with lager, it's easy to not show this by changing the log level.