Issue(KUI-1383): update heading visibility logic to match admin tool preview

[allazis]

This PR contains

• Updates for heading visibility logics to match preview logics in the admin tool in PR for KUI-1343.
• Minor updates of components

Headings are only shown if

• the heading is mandatory (having type mandatory or mandatoryAndEditable)
• it has content and it is mandatory for some (having type mandatoryForSome)
• it has content and it is stored as visible in the database (having visibleInMemo set to true in DB)

If possible when reviewing, please run project locally and compare with ref or kth.se. Example memos to use for comparison:

• DH1623/DH162320241-61063
• MJ2462/MJ246220222-1
• II1306/II130620222-2 (differs because Detailed plan and subsection under standard content in Examination were shown before, although they should not)

E.g. http://localhost:3000/kurs-pm/MJ2462/MJ246220222-1 with https://www.kth.se/kurs-pm/MJ2462/MJ246220222-1

[amirhossein-haerian]

LGTM, Well done, I really liked that you made the code cleaner. I think it is more understandable when you read the code now ⭐️
I tested the code locally as well and it seems great.

[axelbjo]

Looks good to me! Great improvements regarding variable names and structure