Moved density meta to _density

  density meta is no longer persisted.

director.cpp

@@ -1035,11 +1035,11 @@ void Director::SL_densityline(const std::string &line) {
    // what():  [json.exception.type_error.305] cannot use operator[] with a numeric argument with object
    
    std::string sector_text = std::to_string(sector);
-    galaxy.meta["density"][sector_text]["density"] = density;
-    galaxy.meta["density"][sector_text]["warps"] = warps;
-    galaxy.meta["density"][sector_text]["navhaz"] = navhaz;
-    galaxy.meta["density"][sector_text]["anom"] = anom;
-    galaxy.meta["density"][sector_text]["known"] = known;
+    galaxy.meta["_density"][sector_text]["density"] = density;
+    galaxy.meta["_density"][sector_text]["warps"] = warps;
+    galaxy.meta["_density"][sector_text]["navhaz"] = navhaz;
+    galaxy.meta["_density"][sector_text]["anom"] = anom;
+    galaxy.meta["_density"][sector_text]["known"] = known;
     // Add a check to see if density is greater than 500
     // Add datetime stamp
   }