Allow extensionless submissions and do not mangle names

Description

Allows direct-upload submissions to not have a file extension.

Changes

• removed check that required an extension
• do not mangle submission names with the direct-upload: prefix

Additions

N/A

Test and Review

Resolves #252 (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