Add support to package icon.
We need a package icon to display it (in ideascube cards, in potential package selection application, ...)
As we need to display the icon before we download or install the package, this need to be in the catalog metadata.
We agree to add the icon as base64 content in the catalog.
omeka-to-pkg should accept a new option "icon" pointing to (a file ? a url ?), and store it in base64 in the catalog.
Changes in the omeka side will also be needed (user interface, arguments to launch omeka-to-pkg, ...)
Ideascube side issue : ideascube#734