Refactor progress bar and overview

[jochenklar]

This PR aims to:

• Fix the progress bar (Progress bar refers to the first data set only #596)
• Stores the progress in the projects model and updates on saving values (show progress values of subprojects in parent project page (overview of status of multiple projects) #488)
• Shows which pages are fully answered in the overview (Progressbar and answered questions #299, Highlight sections with missing answers #424)

[jochenklar]

Input from @sa-wetter: Numbers should be always show in the progress bar.

[coveralls]

coverage: 80.514% (+0.2%) from 80.339% when pulling 4608efe on refactor_progressbar into ee6bd48 on master.

[MyPyDavid]

think it works nicely in the interview!
It has a lot of logic in the progress.py and looks well-tested.
Is the recursivity really necessary? It will be hard to debug or change, but it works now so...
Ive added a small refactor for the ValueQuerySet manager, maybe this can be used in other places as well..

In the project overview, I would rather have the progess as 15/30 instead of 50% but this can be easily changed.

[MyPyDavid]

Had one more question, it does not update the progress with the Question Autosave or?

[jochenklar]

It does work! Just tested. Can I merge?

[MyPyDavid]

thanks!

[jochenklar]

I changed the view in the projects table to match the string in the interview.