Add setting to allow quicker cancellation of conversion

[bartkessels]

Add a setting that specifies whether or not the user should be prompted with a message asking whether or not the conversion should be cancelled.

Current flow:

1. User clicks on Stop Conversion
2. Application asks if the user really wants to stop the conversion
3. User clicks Yes
4. User stops the conversion

Proposed flow:

User sets a setting to never prompt the user when cancelling

If the setting is set to 'Always prompt'

The Current flow is being executed

If the setting is et to 'Never prompt'

1. User clicks on Stop Conversion
2. Application stops the conversion

[bartkessels]

Fixed in 525156c and 6f5d28f