Replace the fixed-size weightsystem table by a dynamically
relocated table. Reuse the table-macros used in other parts
of the code.
The table stores weightsystem entries, not pointers to
weightsystems. Thus, ownership of the description string is
taken when adding a weightsystem. An extra function adds
a cloned weightsystem at the end of the table.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>