fix documentviewer plone 5 compability

[fngaha]

from version 4 of documentviewer there is a browser folder

[coveralls]

Coverage remained the same at 91.638% when pulling 394f4a0 on fix_documentviewer_plone_5_compability into 5af7b17 on master.

[fngaha]

Do not merge right away because some products (ia.docs) still use version 3.0.3 of collective.documentviewer. It will be necessary to organize oneself to pass there.

I arrived at this observation by doing an integration POC of imio.annex in iA.PST. according to the constraint of having a version lower than the 5 of collective.documentviewer, I obtained the 4.0.1 in which there is therefore now a browser folder for plone 5 compatibility.

I just saw an issue about
#30

[odelaere]

Hi @fngaha ,

Thanks for your contribution :).
Please Add your change in the CHANGES.rst.

Please pin the right version of documentviewer in version.cfg and setup.py (collective.documentviewer>???)
This way we'll avoid incompatible versions upon installing documentgenerator.