Let apt download all packages in one go

[Daniel Holbach]

<dholbach> mvo, would it be easy to let apt download all the necessary packages in one go instead of one by one?
 mvo, if you try the qmldemo example it feels veeery slow - also the remaining-download-estimate will never give you anything remotely accurate :)
<mvo> dholbach: right, we should probably download htem all togehter, I can prepare a branch, essentially we need to adjust dir::cache::archives to the download dir and run cache.fetch_archives()