[refactor] spell handling 
* more config options for spells
  + mind immunity handled by config
  + direct damage immunity handled by config
  + immunity icon configurable
- removed mind_spell flag 
* more use of new spell identifacation

git-svn-id: https://vcmi.svn.sourceforge.net/svnroot/vcmi/trunk@3199 4dfc6b2a-8b31-0410-aa91-d6c70e3ac834