Job duplicates, maximum characters, custom data for Quote

Hi Jarl,

1. I have changed the way how job duplicates being detected. And also fixed the test because it was broken.
Turns out Gengo does not care if similar jobs are being sent as separate submissions. But it detects duplicates if they are sent as one submission.

2. Added ```custom_data``` property for Quote payload

3. Added ```max_chars``` property for Job payload. This property limits the length of translated text. It does not seem to work in Sandbox environment but it works in Production. 

Regards,
Roman