CLI: Better progress reporting

[imobachgs]

Problem

The progress reporting in the CLI was not exactly user-friendly. It started as an experiment during Hack Week, and we did not have the time to look at it again.

Solution

The work on the progress reporting is not finished but at least this PR is a step in the right (?) direction:

• Refactoring, simplifying and documenting the code related to progress reporting.
• Writing a reporting mechanism similar to the one in the web UI (with the same limitations too).

Testing

• Tested manually

Screenshots

Old progress	New progress

What to do

• This mechanism might not work that well when retrying an action.
• Error reporting is still rather poor.
• The main.rs file deserves some love.

[coveralls]

coverage: 72.432% (+0.01%) from 72.422% when pulling 0777161 on imobachgs:better-progress into e8be9bb on openSUSE:master.