* add a `source_reference` field to store message-id
* store the raw content "as is" - there is not preview for this reason (
  because it might be unsafe html or whatever)
* remove proxy roles on scripts. User must have permission.
* minor simplifications

/reviewed-on nexedi/erp5!763

This snapshot were made on Chrome 70 (ChromeOS) with a 1001x932 window
(innerHeight x innerWidth)

To Compare a "screenshot" of a DOM element with a reference snapshot.

This check supports the following parameters:
 *   locator - an element locator
 *   misMatchTolerance - the percentage of mismatch allowed. If this is 0, the
      images must be exactly same. If more than 0, image will also be resized.

https://github.com/niklasvh/html2canvas Copyright (c) 2012 Niklas von Hertzen

from https://github.com/HuddleEng/Resemble.js/blob/v2.10.2/resemble.js © 2013 Huddle

to get stable sort and prevent "random" test failures.

"Restore" sounds a bit strange to me in this context.

So that we can wait for this in the tests

[erp5_officejs] Use upload_dict instead of file_extension to check for correct file-type during notebook upload

Also, exlicitly specify the txt extension during download

/reviewed-on nexedi/erp5!760

/reviewed-on !762

Also, update tests for notebook to check for Upload page

/reviewed-on !764

Fixes rendering when using Chameleon:
  ValueError: only strings can be translated, not: <ERP5Type.Message.Message for ...

/reviewed-on nexedi/erp5!747

/reviewed-on nexedi/erp5!765

adjust font url

This is incubator-echarts-4.1.0-release/dist/echarts.min.js from
https://github.com/apache/incubator-echarts/releases/tag/4.1.0-release

https://www.erp5.com/documentation/developer/guideline/coding/erp5-Guideline.Coding.Best.Practice#use-methods-to-access-properties-in-erp5

Otherwise filling cache fail and it's never used.

/reviewed-on !759