Moved Sign class to worldentities.h/cpp, removed worldhelper.h/cpp.
Renamed Sign class to SignEntity.
Added a method to get all signs and updated mapcrafter_markers.cpp.
Added a getRegionPath method to the world class (for entities cache).
Cheap json/javascript escaping for " chars.
mapcrafter_markers uses proper world dimension and crop.
Fixed some small marker formatting problems.