Workfiles tool add toggle to keep open or close after scene open

[BigRoy]

Is your feature request related to a problem? Please describe.

Prior to #545 the Work Files tool would remain open after opening a scene and after it would auto-close. Some artists prefer to keep the tool open to quickly allow browsing into different scenes or assets.

Describe the solution you'd like

To allow both worlds, and by default auto-closing, I'm thinking of adding an "close on scene open" checkbox that is enabled by default but can be unchecked if the User wants to keep the UI open.

[davidlatwe]

How about also including "scene saved" ? So the checkbox will be like "Close after scene open/save".

[BigRoy]

So the checkbox will be like "Close after scene open/save".

Fine with me! :)