Better support replacing the actual HTTP transport in JS version

[fjenett]

Currently we are using $.ajax in the browsers and a wrapper around http with node.js. This is a start but should also more easily plug into $http with angular and probably others …

[dasantonym]

now implements superagent which behaves quite ok when run through browserify

when refactoring the client code, i'll make sure the transport is abstracted so the client class can alternatively be extended to use a different transport