Allow mail jobs from arbitrary places

[DonDebonair]

Currently, you can only mail (broadcast) reports that are stored in a specific directory ( ~/.athena/reports/). It should be possible to provide a report definition YAML file stored anywhere on your hard disk. Athena should do the following:

1. Check if the passed in file/path exists, and run the report if it does.
2. If it doesn't, check the default reports directory if the report definition exists there.