Change "Restart Chat Session" icon and add a confirmation

[toolmantim]

This changes the current icon from reload (which is too close to a browser reload) to clear-all (which isn't perfect but looks more destructive). It also adds a confirmation dialog:

Before	After

Confirmation

Test plan

• Viewed the button
• Clicked the button, verify prompt cancel does nothing
• Clicked the button, verify "Restart Chat Session" does the action
• Typed /reset and verify it doesn't ask for confirmation

[abeatrix]

Nice!