Added attributes.xml

Used for telling the client about the minimum and maximum amount of
points each attribute can have as well as the amount of points that need
to be distributed.

The listed attributes are only used to validate the correctness of the
character starting points. We could make the client use them, but that
would be at the cost of internationalization.

See http://bugs.manasource.org/view.php?id=501
Add note in some xml files that they are only used by manaplus.
Merge remote-tracking branch 'bjorn/attributes'
Add comments to attributes.xml and charcreation.xml making clear which is used by which client.