Merge branch '37-previews-for-importing' into 'development'

CHANGELOG.md

build.gradle.kts

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

.../java/nl/tudelft/submit/controller/EditionController.java

src/main/java/nl/tudelft/submit/io/GradesImportHandler.java

src/main/java/nl/tudelft/submit/io/ImportError.java

src/main/java/nl/tudelft/submit/io/ImportHandler.java

src/main/java/nl/tudelft/submit/io/ImportWarning.java

src/main/java/nl/tudelft/submit/io/PersonImportHandler.java

src/main/java/nl/tudelft/submit/io/SimpleImportError.java

src/main/java/nl/tudelft/submit/io/SimpleImportWarning.java

...ain/java/nl/tudelft/submit/service/AssignmentService.java

src/main/java/nl/tudelft/submit/service/EditionService.java

src/main/java/nl/tudelft/submit/service/PersonService.java

src/main/resources/application.template.yaml

src/main/resources/messages.properties

src/main/resources/static/js/import.js

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

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

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