start and end date support for every (and more)

Hi!
First of all, thanks for this awesome module. It's great.
Due to my project needs, I have been forced to fork and add a couple of changes:

- every: start and end date support for job executions added, jobs created with every will only run in the date-time interval (if) given. This is helpful as it saves calls to external api's.
- Configuration file conf.js created
- single job types: two jobs with same name but different data will generate two separate records.

Thanks