Add dub project template

[Orvid]

It would be nice if there was a dub project template. Perhaps it could use dub itself to generate the file?

[aBothe]

It somehow always wants to create an .sln file, so creating this even via preset file templates is rather ugly.

[Orvid]

Then we create the .sln, close it, and open the .json. Either that, or we create the .sln, and just never write it to disk...