Improve tokenizing of linkable terms

Improve tokenizing of linkable terms

Currently only tabs and blanks are used for tokenizing the description,
which breaks when a term is at the end of a line or has () appended to
it.
1. Use also other white space characters such as new-lines and carriage
   return for splitting.
2. Remove some common non-word characters from the token before lookup.

Signed-off-by: Philipp Hahn <hahn@univention.de>