Download GeoJSON of completed task

[maning]

Downloading the data for completed tasks will help task creators evaluate the effectiveness of their task:

• timeline of progress
• effectiveness of error/task creation, i.e. is the OSMLint validator catching the correct error or is there too much "Not an error" reported?

@ajithranka @Rub21

[Rub21]

This is great idea!!!, i will implement it on to-fix

[Rub21]

@maning @ajithranka, I think this is done for the back-end side,for example : missing cardinal in motorway link https://build-to-fix-production.mapbox.com/tasks/missingcardinalinmotorwaylink/v1/items form to-fix task https://osmlab.github.io/to-fix/#/task/missingcardinalinmotorwaylink