Handle non-parsed tags in xinp-files

[VikingScientist]

A very frequent error is wrong syntax in the xinp files. Tags which are not registered are simply ignored which means that you never get notified when your solution is misbehaving since you wrote <stabilisation> instead of <stabilization>.

The user needs to be sufficiently warned when there is something wrong with the input file by either stopping program execution or issuing a clear warning message; preferably at the end of the output for increased visibility.