added saving of execution
    * execution through workflow completed
    * additional saving of headers, data, request method
    * removed GET /workflow/xxx/execute, created POST /workflow/xxx/executions -> more REST like
added possibility to execute single apicalls
    * execution of single api calls
    * list all executions of an apicall
added executedAt to single api call executions
Automatically updated the groc documentation via drone.io