Progress dialogue when adding data to a scan

[tjkuson]

Describe the solution you would like
Add a dialogue with a progress bar to display feedback and progress of adding a scan to the library.

Describe alternatives you have considered
Could send to a jobs widget, but that would not cohere with the rest of the project (we use pop-up dialogue for everything else). A jobs handler could be a good long-term goal, however.

[tjkuson]

This is taking longer than expected due to a major refactor of how actions work. The issue was closed by accident.

[tjkuson]

#52 adds a basic dialogue, but lacks the features mentioned in the issue. This is low-priority at present. However, adding the features should be simple (it is a matter of coping the code from the download runner and dialogue).