[RFE] pull locally chunks from a remote store

[giuseppe]

I'd like to mirror all the chunks pointed by an .idx from a remote store to a local store, something like:

casync pull-local --store http://web/store.castr --extra-store /some/thing/else --seed /already/extracted/tree foo.idx /destination

[garyvdm]

Somewhat similar to issues #177 and #158 .