check_submission_allowed messages all have the same severity

[khattam2]

Fixes #1226

Description

What?

check_submission_allowed messages all have the same severity

Why?

submission_check is given a flag whether it should print the strings as errors or warnings but this does not make sense

How?

The flag has been removed and severity is decided by the statement.

Testing

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• Accessibility test using the WAVE extension.
• Django unit tests.
• Selenium tests.
• Other test. (Add a description below)
• Manual testing.

[ADD A DESCRIPTION ABOUT WHAT YOU TESTED MANUALLY]

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Translation

• Did you modify or add new strings in the user interface? (Read about how to create translation)

Programming style

• Did you follow our style guides?
• Did you use Python type hinting in all functions that you added or edited? (type hints for function parameters and return values)

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Is it Done?

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• After the review, the developer has made changes accordingly
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[ihalaij1]

This PR requires some more changes to correctly classify and display error/warning/info messages from functions one_has_submissions() and one_has_access().

I will be making these changes myself.