10 fix add plaso timeline script

## Make add timeline script better
The add timeline script is a hack, and will always be until we have a proper Plaso frontend. But until then let's have a script that works.
Adding argument parsing and some error handling. This fixes issue #10

Reviewer: @joachimmetz

Yeah, this is the Django way of doing this. Django is doing try, except ObjectDoesNotExist behind the scenes. I do it out of habit. I now also catch properly if create fails.