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/TimeFilter.cpp

@@ -210,7 +210,7 @@ namespace ATC {
       }
       else if (filterType_ == STEP_FILTER) {
         newTimeFilter = new TimeFilterStep(*this); 
-      } else newTimeFilter = NULL;
+      } else newTimeFilter = nullptr;
     }
     else { // default to return base class
       newTimeFilter = new TimeFilter(*this);