Add task filters

[wgergely]

Add a dropdown menu for to the UI to help set ShotGrid task text filters in the assets view.

Currently asset list items are clickable pressing the shift/alt modifiers and pressing a text segment on the item's name. This will set/add a positive or negative filter to the text filters but the system is somewhat clunky. Having a bespoke menu to set filters explicitly would be easier to use and possibly faster also.