Remove Bootstrap dependencies

A lot of styles are inherited from bootstrap.

Migrating the tokens and defining the base theme will already remove relying partly from bootstrap base styles.
However, it is unrealistic to migrate away from bootstrap css in one-go.

The idea is to progressively migrate the css, bootstrap tokens, into using our own base-theme.

**Example deactivating bootstrap wildly**

Some components heavily relying on Bootstrap at the moment should remain untouched until they are fully reworked or most of bootstrap basics have been removed (cf Members/Groups/roles). Their migration is not hard but time-consuming and for now low prio.

Taking the nav bar as an example, the steps to get away from bootstrap would be:
1. `d-flex -> flex` uses tailwind directive
2. `align-items-center` -> `items-center` custom css/bootstrap classes uses tailwind directive

Example `NavSubLink`:
```
Before
import React, { FC, ReactNode } from 'react'
import { LinkProps, NavLink } from 'react-router-dom'
import { IonIcon } from '@ionic/react'
import classNames from 'classnames'

type NavSubLinkType = LinkProps & {
icon: string | ReactNode
children: ReactNode
}

const NavSubLink: FC = ({ children, icon, ...rest }) => {
return (

export default NavSubLink

After
const NavSubLink: FC = ({ children, icon, ...rest }) => {
return (