Progress UI: issues in presentation of "Stop" action

I'll be updating the changes as I figure them out

Feel free to add commits if you manage to do it before me!

Commit 1/2: progress-info-widget: Change cancel button tooltip 

• Change tooltip text from "Stop Operation" to "Cancel" to be less wordy

Before	After

Commit 2/2: progress-info-widget: Change cancel button icon

• Remove tooltip text when an operation canceled
• Set icon "cross-filled-symbolic" when cancel operation called by user
• Set icon "emblem-ok-symbolic" when an operation is completed
• Add tooltip "Completed" when an operation is completed

Before Before_fix.mp4	After Final_fix_fin.mp4

Do let me know if any changes need to be made

Marking this as ready

See #3294 (closed)