xhr request is not properly implemented

[w-a-b]

The callback-implementation of adapter-xhr seems to have several issues:

1. payload.headers is not set on the request (missing something like for(let key in payload.headers){xhr.setRequestHeader(key, payload.headers[key])}).
2. Instead payload.headers is set on the result-object (res) (where probably e.currentTarget.getAllResponseHeaders() is meant to be set).
3. setResult is not provided by the invoking apicase.js, so it always fails with "Uncaught TypeError: setResult is not a function at XMLHttpRequest.xhr.onprogress".