* Replace jQuery with SuperAgent which works in both Node.js and browser
* Use UMD pattern (returnExports.js) to make the module exporting compatible
with all major systems: AMD, Node.js (CommonJS) and browser
* Implement support of header and form parameters. Closes#1736
* Move HTTP requesting code to `ApiClient` and allow customizing options
in it, e.g. "basePath"
* Update unit tests accordingly and add some tests for `ApiClient`
