Fix submission result responses being too big or empty

Description

Fixes submissions returning most entities multiple times, leading to responses big enough to make Spring stop working once again.

Changes

• The submission controller returns entities instead of entity containers
• The getAllChildren getter is marked as @JsonIgnore so Jackson (which is the library that Spring uses) ignores the setter while serializing

Additions

None.

Test and Review

Closes #166 (closed)

To be filled in by the reviewers

• All of the methods are commented to expectation

• The methods are tested to satisfaction

• There are no unnecessary files present in the MR

• The continuous integration has no problems with the MR

• The MR is filled in as requested (including labels, milestones, and reviewers)

• The documentation is up-to-date

• All nullable parameters are marked as such