Add possibility for multiple Jobs to have identical filenames

Problem
For now there is no possibility for Jobs to have identical file names even if their content is identical.

Possible solution
It's possible because of changes in SmartlingTranslator::getFileName() method: it generates file name like item_label + item_type + item_id for jobs where amount of job_items is less or equals 3 and like item_type + item_id for others jobs.

Existing problem
Patch works fine for uploading files: in Smartling dashboard we can see (in one file) authorized strings to many locales. But as for download process we have an issue The imported file job id new_job_N does not match the job id old_job_N.. This limitation comes from tmgmt module and we need to think how to deal with it.