T2345: Replace instances of NULL with nullptr

The following changes have been applied to src and lib folders:
regex replace: ([^"_])NULL ⇒ \1nullptr (8968 chgs in src, 1153 in lib)
Manually find/change: (void \*) nullptr ⇒ nullptr (1 case)
regex find: ".*?nullptr.*?"
  Manually ~14 cases back to "NULL" in src, ~2 in lib
  regex finds a few false positive where nullptr appears between two
  strings in a function call

lib/atc/InterscaleOperators.h

@@ -277,7 +277,7 @@ namespace ATC {
     data * return_quantity(std::map<std::string,data * > & list, const std::string & tag)
     {
       typename std::map<std::string,data * >::iterator it = list.find(tag);
-      if (it==list.end()) return NULL;
+      if (it==list.end()) return nullptr;
       return it->second;
     }
 
@@ -310,7 +310,7 @@ namespace ATC {
     {
       typename std::map<std::string,data * >::iterator it = list.find(tag);
       if (it!=list.end()) return it->second;
-      return NULL;
+      return nullptr;
     }
 
     /** helper function to force the reset of all data in a list */