Bug #799 Enchanting window area slider

http://bugs.openmw.org/issues/799
Area slider is now visible in touch and target mode, and resets to 0 if self is chosen, so the cost i calculated correctly. Every change in the spell effect dialog changes the costs instantly (before the cost was shown only after pressing OK).

Note, that constant enchantment part is left untouched, because I don't know yet how it works in vanilla (absorb health on self and area?!).