When a collection is created, users need a way to add new articles to it.

• On both, expanded and collapsed collections there is an add action available. It will open a search panel to find an article. It is the same dialog as used in T111094.
• Once an item is added, from it's action menu (dropdown), an option should be available to remove from the current collection.
• Items in any group (for later, collections or suggestions) will have an action menu from which they can be added to an existing collection.