Remove Sidebar from joinGroup

[Daniel Zoller]

the sidebar lists the groups of the logged in user. In my point the list is unnecessary.

[Daniel Zoller]

also remove the code that retrieves the groups from the controller

[Thomas Niebler]

fixing #2640 The JSPX only retrieves the groups from the context.loginUser, so we don't have to do anything about the controller.

→ <<cset abb7a2dcd971>>