Merge branch 'development' into '150-configure-last-submission-all-submissions-grading'

...va/nl/tudelft/submit/controller/SubmissionController.java

src/main/resources/messages.properties

src/main/resources/scss/drag-and-drop.scss

src/main/resources/static/js/drag-and-drop.js

src/main/resources/templates/assignment/submissions.html

src/main/resources/templates/assignment/submit.html

src/main/resources/templates/assignment/view.html

src/main/resources/templates/edition/student.html

src/main/resources/templates/group/view.html

src/main/resources/templates/layout.html

src/main/resources/templates/submission/content-overlay.html

src/main/resources/templates/submission/content.html