Added documentation to functions and column names.
Created functions to generate a log entry for a given job_id.
This is so we have a uniform way of generating this entry.

Added a run_job function which will run the job given its job_id or jl_id
regardless of timeouts and enabled state. Useful for debugging and as a building
block for the workers to execute the jobs.
Merge pull request #4 from zalando/data_model

Added documentation to functions and column names.