[FEATURE] Add support for adding an asset to a playlist.

[nicomiguelino]

Problem

• Saving an asset via the browser extension only adds it as a content but doesn't add it to a playlist.

Proposed Solution

• Give users the option to add it to a playlist before clicking the "Add to Screenly" button.

Alternative Solution

• TL;DR: Aske for user inputs incrementally. In the first page/view, ask the user from a playlist (from a list of options, if there are playlists created for the logged in user). Show the "Add to Screenly" button on the next page/view.

[vpetersson]

Nice idea.