Reference picker shortcut panel: pinned folders

[tusmester]

As a user I'd like to pin certain folders in reference picker that I use frequently. I want to see these pinned folders on the shortcut panel anytime I open a reference picker.

• pinned folders are user-specific, can be saved locally (no backend save for now)
• pin a folder: from the picker's grid itself, using a button
• unpin a folder: from the shortcut panel with a button