NIEDUUI-126: Migrate "Search & Invite Groups"

[TomlDev]

https://schulz-informatik.atlassian.net/browse/NIEDUUI-126

Backend Changes

• Fix im-/exporting of modules
• Add classManagement module to get class members by group path
• Remove obsolete types
• Move conferencing types
• Add groups module to fetch data from keycloak
• Move fetchUsers from user service to groups service

Frontend changes

• Fix index.scss missing generic default font-family
• Fix styling of frames
• Extracted the formSchema from the conferencing dialogs
• Implement the group search/invite

Additionally fixed

NIEDUUI-305: Conferencing throws errors on every request

What is missing

• Test for the new modules (will follow in next PR)
  • classManagement
  • groups