Merge arender addon and package repositories

We want to merge the two arender repositories as we're gonna release them at the same time.

Addon and package version will follow the current package versioning.
https://github.com/nuxeo/nuxeo-arender-connector
https://github.com/nuxeo/marketplace-arender-connector

The ticket contains also the following fixes:

• Add repage option to ImageMagick commands in rendition
• fix nuxeo.url retrieval within OCP