[FIX] invoice_xunnel: Documents Thumbnails
This MR needs the merge of the MR !93 to keep the tests from fail, and is a solution for the issue #59
- Change thumbnail date, from the sync date to the stamped date.
- Add Name's document and Total Amount inside the thumbnail under the title.
- Total and Emmiter name are now searchable in the documents view.
- Add help for the fields in the model "ir.attachment"
- Add translations for the help and name of the fields.