Set a default selection for a portfolio

[benel]

A portfolio could be set so that the initial selection is no more empty but is related to corpora, topics, and maybe attribute values.

For minimal impact on the Hypertopic model, it could be set by admins in the config file.

It was one of the solutions proposed to reduce initial loading (and display) time.

Phase 1

• [ ] Scenarios (Gherkin)
• [ ] Mockups
• [ ] Implementation strategy

Phase 2

• [ ] Acceptance tests (Capybara)
• [ ] Implementation

Phase 3

• [ ] Screencast