As fetch.go was the only consumer of go.rice, it could be safely removed in favour of go-bindata and go generate.
Motivation to do that was the fact that go.rice throws panic in iOS when compiled with gomobile.
This PR adds Fetch API and fixes#289 by using concurrency safe Otto VM wrapper wherever it's possible. This involves new package geth/jail/vm that is used by jail and by our forked ottoext/{fetch/timers/loop} packages.
It also adds more tests that are supposed to be run with --race flag of go test.