Improved json validation
- split JsonNode.cpp into JsonNode and JsonDetail files
- validation should be notably faster (at least 10% faster loading)
- support for "format" field, allows checking existance of files.
- minor fixes in schemas
- msk/msg files are now optional

git-svn-id: http://svn.code.sf.net/p/vcmi/code/trunk/@3597 4dfc6b2a-8b31-0410-aa91-d6c70e3ac834