1306 usercontext menu inconsistent padding

[YiranDuan721]

Motivation and Context

To improve the look of the user menu.

Description

1. Align padding of header and items in the menu (fixes #1306)
2. Reduce the space between icon and text in each item button
3. Adjust the size and position of theme selections, making them more like sub-items of the item "theme" in the menu

Step for testing

1. Remove "web/assets/css-dist"
2. Run npm i under "web/"
3. Run DB from docker; Build and run TUMLive-Backend
4. Access localhost:8081, clear all website data and refresh website

Screenshots

Before	After

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Logins

| Kurs1 | Kurs2 | Kurs3 | Kurs4 | | ---------------------------------------- | ------------------------- | ------------------------- | ------------------------- | | public | public | loggedin | enrolled | | prof1 | prof1 | prof2 | prof1
prof2 | | student1
student2
student3 | student1
student2 | student2
student3 | student1
student2 |

[YiranDuan721]

I think the Admin Button is still slightly off.

Thank you, I've made one more change. What do you think of this:

[SebiWrn]

I think the icon is still a bit more on the left than the other icons

[YiranDuan721]

I think the icon is still a bit more on the left than the other icons

Yes indeed... They should be vertically aligned in the center now: