Add download button to the NFT detail

[vikiival]

It would be nice to have separate download button for the main nft asset.

The button only shows when the user is owner.

h/t @deeplogic

[jkdizajn]

I want to take a picture of the cake nft and the download button will have its recipe :)

[yangwao]

maybe we can combine it with #219 ?

[roiLeo]

Meanwhile