Issue #340 - rework ProgressBar to support non-upload scenaria and stacks
Issue #340 - add javadocs and make it easier to have a ProgressBar with a single (default) stack
Issue #340 - Add tests for ProgressBar
Issue #340 - Minor cleanup before PR review
Issue #340 - Make UpdatableProgressBar a specialization of ProgressBar
Issue #340 - Simplify UploadProgressBar to duplicate the logic from ProgressBar as less as possible

Improve the test case for UpdatableProgressBar
Issue #340 - Move #createLabelModel() to be a method of the Stack itself.

Add a sample.
Issue #340 - add checks for the value of the progress
Issue #340 - extract Stack as a proper class.

The users have to use ProgressBar#getStackId() explicitly now
Merge pull request #361 from l0rdn1kk0n/340-progress-bars

Progress bar rework