New API type for group applications

Having developed on a new application, CashIT, I saw that the INFO API type would not be enough for this use case. According to the current design, the application must be able to:
- **Fetch the name of any group**
Allows the name of a group to be displayed in tables when the current user is not a part of that group
- **Fetch the members of any group**
This information is needed so that forms can be pre-filled with the members of a group
- **Fetch the name of any member**
This information is needed so that tables can be filled in lists

There are probably more use cases here, but I probably forgot about them.

The reason that this needs to be done on an API-level is that in this case, the division treasurer should be able to make changed on behalf of another group.

I propose a new API type with the following endpoints:

- `/group` - Get information about a group. The data structure could be as follows:
```ts
{
id: string;
name: string;
prettyName: string;
groupMembers: {
id: string;
nick: string;
firstName: string;
lastName: string;
}[];
superGroup: {
id: string;
name: string;
prettyName: string;
type: string;
}
}
```
- `/user` - Get information about a given user
Same structure as `/user` is today on the INFO API type