Namespace the javascript files under vertx, e.g. vertx/http

This prevents conflicts with other JS libraries such as node.js where the API is (wrongly, I believe) at the top level. So now, instead of `var http = require('http')` you write `var http = require('vertx/http')`.

This is a good time to make this change, I believe, because the JS api is changing from `load(...)` to `require(...)` so users will have to be mucking in this area of their JS anyway.