Moved the job name from basic to the common options.
Delete the local scratch directory if it exists (should not with the
auto-generated job name, but it might be there if the user specifies the
name manually).
Added job_name to yet another list.
More descriptive help.
Added tests for --job-name.
Handle the case where job_name is set to an empty (or whitespaces only) string.
Updated the documentation with --job-name.
Merge pull request #956 from david-cliqz/job_name_parameter

Added a job-name parameter. Resolves #955.