Login should not take the user to the front page

[khattam2]

Fixes #1133

Description

What?

Login should not take the user to the front page.

Why?

The user should be redirected to the same page they came from after login.

How?

The user is now being taken to the page it came from before logging in.

Testing

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What type of test did you run?

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

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Did you test the changes in

• [ ] Chrome
• [ ] Firefox
• [ ] This pull request cannot be tested in the browser.

Think of what is affected by these changes and could become broken

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)

Have you updated the README or other relevant documentation?

• [ ] documents inside the doc directory.
• [ ] README.md.
• [ ] Aplus Manual.
• [ ] Other documentation (mention below which documentation).

Is it Done?

• [ ] Reviewer has finished the code review
• [ ] After the review, the developer has made changes accordingly
• [ ] Customer/Teacher has accepted the implementation of the feature

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[murhum1]

I figured it might be better to build the redirect url on server side instead, to avoid extra JS on every page, and for the (unlikely) event where the logout url would change for some reason. Also added the next-parameter to the mobile login link.