also update test for unhandled libreoffice 5.2 formats

Force the use of wkhtmltopdf if:
- source format is html
- destination format is pdf
- conversion_kw is not empty

- keeping backward compatibility
- using getAllowedConversionFormatList
- deprecating getAllowedExtensionList

/reviewed-on nexedi/cloudooo!9

Originaly, the y format (docy, xlsy, ppty) is a file extension that is use by an OnlyOffice document.

An OnlyOffice document is composed by : 

- a file with extension in (docy, xlsy, ppty)
- a separate media folder containing media files (Ex: media/image1.png)

Several problems : 

- Two documents cannot be in the same folder
- How to send / get from Cloudooo to ERP5 ?
- The document cannot be stored easily in ERP5 (embedded files ? seperate images linked to the document by predecessors ??)
- How to download an OnlyOffice document from ERP5 ? How to load it on OfficeJS ?

To solve, we embbed all the files composing the document into one zip (like docx, odt, ...) : 

- Two documents can be in the same folder
- We send / get from Cloudooo as usual with portal transform
- The document can be stored in File data in ERP5 like any other docx document.
- document.getData allows to download the document data and JSZip can be used to extract easily the body in OfficeJS.

To keep backward compatibility, a docy can be : 
- the OnlyOffice document body (`startsWith("DOCY;v2;")`)
- can be a zip file (`startsWith("PK\x03\x04")`) containing one file at the root of the archive + optional media folder

/reviewed-on nexedi/cloudooo!8

except critical parameters:
- simple switch handled
- switch with string/number argument handled
- switch with url/path/basename argument handled by giving data

/reviewed-on nexedi/cloudooo!6

that can happen on the environment where UNO library is built with Python 2.

/cc @rafael @gabriel @kazuhiko 

/reviewed-on nexedi/cloudooo!5

unnecessary space change removed

So that both readme and changelog automatically render well on

https://lab.nexedi.com/nexedi/cloudooo  and on  
https://github.com/Nexedi/cloudooo

CHANGES is also renamed -> CHANGELOG along the way, because that's what
gitlab autodetects as changelog file name:

https://lab.nexedi.com/nexedi/gitlab-ce/blob/827d3914/app/models/repository.rb#L353

/cc @kazuhiko, @gabriel

/reviewed-on nexedi/cloudooo!3

writer_png_Export filter now works but draw_eps_Export and impress_eps_Export do not work.