cmd, console: split off the console into a reusable package

cmd/geth/accountcmd.go

cmd/geth/chaincmd.go

cmd/geth/consolecmd.go

cmd/geth/consolecmd_test.go

cmd/geth/js.go

cmd/geth/js_test.go

cmd/geth/main.go

cmd/geth/run_test.go

cmd/geth/usage.go

cmd/utils/flags.go

cmd/utils/jeth.go

console/bridge.go

console/console.go

console/console_test.go

console/prompter.go

console/testdata/exec.js

console/testdata/preload.js

internal/jsre/bignumber_js.go

internal/jsre/completion.go

internal/jsre/completion_test.go