correct conditions.
All custom conditions are now validated using schema.
Note that some of scenarios may not work due to instant win/loss, mostly
because some placeholders fail to import (Mantis #1643)
campaign:
- new file MapFormatJson that implements small subset of Json map
format, as described on wiki
- vcmi will read overrides from file config/mapOverrides.json (currently
empty)
- Json writer for logical expressions
TODO: write data for map overrides
