Jira: issue changelog download, multithreading

**Changes:**
- issue changelog download
 -  is optional 
 - added an additional node output with changelog
- multithreading
  - mightily improved performance
  - default 50 threads (it might seem unreasonably high, but the choke point here is the time for jira to answer)
  - number of threads can be changed
- adjusted the progress indicator for recent changes