Issue history download

- issue history download is now possible
- will be added as an extra node
- added checkbox on dialog
Merge remote-tracking branch 'upstream/dev' into dev
Fix for "Output spec-array length invalid: 1 <> 2"
Introduced multithreading
Added progress indicator; refactoring
Cleanup, `RsClient` is no longer connected with `UriBuilder`

Removed connection `JiraOnlineAdapterRsClient` with
`JiraOnlineAdapterUriBuilder`
JUnit cleanup
Added an option to set thread count
Merge pull request #134 from qmar/dev

Jira: issue changelog download, multithreading, DEP-6