improve configuration API
improve configuration API

attempt to compute a default root for loading resources:

  * for the browser, if smoke is being run from node_modules/bd-smoke,
    then it's the owning project directory (node_modules/..); otherwise
    it's the path of the URL

  * for node, if smoke is being run from node_modules/bd-smoke,
    then it's the owning project directory (node_modules/..); otherwise
    it's the current working directory at the time node was invoked

decouple configuration from defaultStart

altoviso/bd-smoke,altoviso/bd-smoke,altoviso/bd-smoke