EP: Use same portfolio entry in multiple portfolios

In many cases users would like to use the same portfolio entry the created in multiple maps, e.g. to present themselves with a CV or they hobbies etc. This is currently not possible, a portfolio entry is always linked to only one portfolio. 

There are several issues to solve: 

• Implement multi-relation data model (one relation might be the primary one if needed)
• Implement GUI to import an existing portfolio entry to another portfolio from within the entry
• Implement correct handling of publishing and editing workflows
  • In portfolios with different states the most restrictive portfolio wins (entry is closed in one portfolio, it can not be opened in another one).
• Address questions regarding data protection privacy 
  • visibility of comments made in another portfolio?

If needed the feature of multi-referencing can be limited to self-created portfolio entries and portfolios and not be allowed for templated based portfolios

Details TBD