In particular, this changes the order so that the instance gets created
before downloading the mods (like other install tasks), and the mod download
directly puts the files in the staging folder (like the others), instead
of that weird makeCached and copy stuff.
This fixes some issues with modpack downloads from FTB, like creating an
instance with no mods in it.
Signed-off-by: flow <flowlnlnln@gmail.com>
