Remove portal: Showed upcoming exams but did not work in new OpenOLAT versions

Can be reinstalled by reverting this commit.
Remove last bits of the home portal (upcoming exams)

See last commit for more info
get xman ready to work with OpenOLAT 8.3.5, changes the first few problems
Revert some files, where @Klemens got a better solution
Merge remote-tracking branch 'origin/update_8.3.5' into tmp
Completed update to OpenOLAT 8.3.5 (now compiling and working!)

Mainly cleand up the messy email sending code