[$20] Improve UX for Close Task button

[ajefts]

The existing button to close a task is giving some people the impression that it is "canceling" it. Let's update the UI a bit.

1. Rename the button to "Mark Complete".
2. Add hover text to the button that says "This will close the task and generate a payment for the assignee and copilot."
3. Let's try a green button color.

[ajefts]

@vikasrohit Another potential simple one for WM UI updates.

[ajefts]

fyi @vikasrohit I think maybe we can do this as part of #1174?

[maxceem]

Challenge https://www.topcoder.com/challenges/61196f05-e57f-4736-b08c-a715403d9dee has been created for this ticket.

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[phead198708]

Hi,

The bot is ok now.

[Vips19]

@bug-bash-helper assign