Make it more go packaging friendly.

@jiayliu @tkchin

Based on https://golang.org/doc/code.html and looking at other go packages like [docker](https://github.com/docker/docker) I think this is a little more *go friendly*. 

It also makes thing easier to get up and running. But it's a bit of a development change.

When you wanted to start developing you would do,

```
go get github.com/googlechrome/webrtc/samples/web/content/apprtc/collider
```

then you would edit source in the `$GOPATH/src/github.com/googlechrome/webrtc/samples/web/content/apprtc/collider` directory and edit right in there.  then as you make changes you can do,

```
go install github.com/googlechrome/webrtc/samples/web/content/apprtc/collider && collider
```

which will run your local version. 

basically Go looks at `$GOPATH/src` first and uses whatever is there unless it doesn't exist in which case it tries to git clone it.

Let me know what you guys think here.