[#2036] Add tab-design for login page

[jiromaykin]

issue: https://taiga.maykinmedia.nl/project/open-inwoner/task/2036
Differs a bit in design from the tab we have in 'Mijn uitkeringen'

Log in options are now split in multiple tabs (but Login URL stays the same):
https://www.figma.com/file/iKGhWhstaLIlFSaND2q7cE/OIP---Designs-(new)?type=design&node-id=270-6788&mode=design&t=DpALupfBX7lYWPsm-0
Clicking on "Log in met e-mail adres" will show the hidden log-in form.

Direct link from the outside for business users is ".../accounts/login/#zakelijk" because the leading slash indicates the root of the URL path, and the hash anchor is appended to it.

Also added two new views:
- http://localhost:8000/accounts/login-business/
- http://localhost:8000/accounts/login-email/

Removed urls/views again.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.07%. Comparing base (8e638a5) to head (dfd16d9).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #992   +/-   ##
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  Coverage    95.07%   95.07%           
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  Files          955      955           
  Lines        33961    33961           
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  Hits         32288    32288           
  Misses        1673     1673           

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[Bartvaderkin]

Note: I tried fixing the tests but I'm not sure if we cover every login option (there are quite a few combinations of digid, eherkenning and admin with and without OIDC, plus the regular email login). For each case we need to test multiple situation (new user, updating user, existing email etc) but they get lost in boilerplate.

[Bartvaderkin]

Feedback for later: Django URL's are technically dynamic so we don't want hardcoded URL's in the Javascript (or HTML, CSS etc). This is why there are {% url "xyz" %} and {% static 'xyz' %} in the templates (to reverse() the URLs from whatever is in the urls.py's).

So these Link selectors should be different and not use the href=, but a class or id (possibly chain a .querySelector() from the Tab elements you grab by ID just below)

[jiromaykin]

OK, @Bartvaderkin I will have to create new id's/selectors here because the tabs are not inside those panels-with-id's;
they are elsewhere in the HTML structure.

[Bartvaderkin]

Feedback for later: The queryselector has a forEach() so you can just chain from that:

document.querySelectorAll(LoginFormFocus.selector).forEach((element) => new LoginFormFocus(element))

[Bartvaderkin]

😉

[Bartvaderkin]

This doesn't work as the tabs have the path AND a hash as href now.

And in general I feel it is better to not select on href like this because it often has these issues with unexpected dependencies here or there. (see also the earlier note about LoginForm.js)

[Bartvaderkin]

I appended some fixes to the urls in login.html (the next url wasn't applied to both the text and icon url, and some urls were hardcoded).

I also added some comments for later (most just code style, one possible issue but it is not an important feature and doesn't seem to come up in normal use).

I also checked the conditionals so I think this is good to go for acceptance.