Custom function sample using web worker

New web worker sample (#96)

* initial draft from Shaofeng

* add copyright headers

* rewrites to readme with images

* renaming job variables for clarity

* added UI animation for reference

* small code and comment cleanups

* added correct button icons

* added correct button icons

* update image

* Fixes and cleanup work to readme

* update manifests

* created cleaner localhost references (#97)

Co-authored-by: David Chesnut <davech@microsoft.com>

Co-authored-by: Maarten van Stam <aafvstam@users.noreply.github.com>