Refactor|World|Sector: Implement Sector-linked MapElement iterations with C++11 lambdas
Map Renderer|SurfaceDecorator|Client: Cleanup
Fixed|DED|libdoomsday: (Record::operator []) Variable 'execute' not found

Occurred when regression testing jimi's old "Hell City" mod. Caused
by a typo in defn::Sky::addModel()