Add configurable display names to items

[wgergely]

As Bookmarks wraps around different pipeline folder structures, the display names of items become somewhat uncontrolled.

E.g. if an asset is called SH010_0010 it will be displayed as SH010_0010. However, if the asset is nested, the display name might end up being SEQ010/REND/lighting/SEQ010_SH010_lighting. which is not what we'd want necessarily. It certainly makes it harder to parse the item names visually for the user.
I think we can add two new columns to the bookmark database to configure the Qt.DisplayRole string of the bookmark item and the assets within it using the tokens module.