Single xml solution - compatibility with skill-set and special-set

Mana-mantis: #506.
Bumped protocol version to 3

This is so that master and lpc2012 use the same protocol again,
where starting attributes are sent on character creation.
Hide attribute sliders on character creation when appropriate

When the minimum and maximum values of the attributes are equal, then
there is nothing for the player to customize and the sliders are not
shown.

At the same time the dialog has been fixed to resize properly to any
number of modifiable attributes.