Implement Nuxeo Partner Certified Addons

Context : 

Nuxeo Partner Certified addons needs to be categorized within the Nuxeo Marketplace.

Currently, we don't have any property storing this information, so we indicate in the package name the certification status (see https://connect.nuxeo.com/nuxeo/site/marketplace/package/onlyoffice-nuxeo?version=1.0.0 for example).

The Nuxeo Certification program is detailed in https://partners.nuxeo.com/nuxeo/ui/#!/doc/5786e847-f824-423e-ad32-c510bc0d0661

To do  :

Create 'Partner Certification Level' data field for packages 

It will have one of three values, as a dropdown field 

• Premier certified
• Standard certified
• Not Certified

Same format as the 'Featured' field, see attached 

Other info 

• This property is available in the marketplace edit form, not in the package.xml (so that package publisher can't self certify their add-ons)

• Only nuxeo people can edit this property
• The property should default to Not Certified  

AC

• I will go into a package using a Nuxeo account, I should be able to edit this property and have only three options
• I will choose a packages that have not been edited, it should have the relevant property as Not Certified
• I will access the package page from a non-Nuxeo account, iI should not be able to edit this field