allow depends_on to be a job id or a job itself

Other parts of the code (i.e.: the `.create()` method) allow the `depends_on` kwarg to be a `Job` object *or* a job id. This is an attempt to allow that same idea within the `.enqueue_call()` method for a queue. Since this part of the code requires actually knowing the precise redis key for the job that's depended on, my intuition is that a `.fetch()` is the only way to solve this.
use internal job_class for check
add PyCharm .idea folder to .gitignore
test for id based job dependancies
Merge pull request #445 from conslo/patch-1

allow depends_on to be a job id or a job itself