[WIP] coreapi: pubsub, dht, swarm

[magik6k]

TODO:

• Tests
• Cleanup a bit
• Review

I'm not sure what to do about the dht api - the commands expose some very verbose information which seems only useful for debugging, and I want to keep the api as simple as possible.

[magik6k]

Random test fail in coreapi dht tests:

--- FAIL: TestDhtFindPeer (0.02s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x48 pc=0x176e347]

goroutine 60 [running]:
testing.tRunner.func1(0xc4200fef00)
	/Users/travis/.gimme/versions/go1.9.darwin.amd64/src/testing/testing.go:711 +0x2d2
panic(0x1865da0, 0x203d7b0)
	/Users/travis/.gimme/versions/go1.9.darwin.amd64/src/runtime/panic.go:491 +0x283
github.com/ipfs/go-ipfs/core/coreapi_test.TestDhtFindPeer(0xc4200fef00)
	/Users/travis/gopath/src/github.com/ipfs/go-ipfs/core/coreapi/dht_test.go:29 +0x247
testing.tRunner(0xc4200fef00, 0x1aca698)
	/Users/travis/.gimme/versions/go1.9.darwin.amd64/src/testing/testing.go:746 +0xd0
created by testing.(*T).Run
	/Users/travis/.gimme/versions/go1.9.darwin.amd64/src/testing/testing.go:789 +0x2de
FAIL	github.com/ipfs/go-ipfs/core/coreapi	0.114s

This (FindPeer) and FindProviders seems to fail in about 1 out of 20 cases for me, not sure why.