Trim names and short names

We should discuss whether we should integrate calls of strip in the import code to clean data like 5a . We watched some issues with wrong data like this in production while importing current student data.

Implementation note: Add a converter for stripping spaces (lstrip, rstrip and strip, separately). Then, change converters so they can be chained: The converters of an import field need to be an array, and then all converters in the array are applied one after another.