[Sections] Allow to collect all submissions for one section when the collection date for that section has passed

[NelleV]

Right now, graders can create a submission by hand when the collection date for a group has been passed. We need to automate that.

[NelleV]

I'm adding this to milestone 1.1.0. This functionnality would be very useful for ECN, when grading labwork. There are about 12 groups. Between the first group and the last, often a couple of week goes by. Right now, the graders need to wait until all the groups are done with the labwork before grading.

Also, the submission view needs a bit of love. I think implementing this may imply spending a bit of time refactoring the UI of this view.