refactor(core): NewIPFSNode constructor

this is a dirty hack

fix: remove merkledag import

may need to squash this commit into the merkledag move commit

NB: all commits (from master) pass tests up to this point.

fix: squashme into use core constructor

early out if no entries in wantlist

Implement ipfs ping

core: make sure to call swarm.FilterAddrs

also move network setup into its own self-contained func

linkblock size calc test

osxfuse: fix version check