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/ConcentrationRegulator.cpp

@@ -186,14 +186,14 @@ const double kMinScale_ = 10000.;
      ConcentrationRegulator::ConcentrationRegulatorParameters & p)
       : ConcentrationRegulatorMethod(concReg), 
         concentrationRegulator_(concReg),
-        interscaleManager_(NULL),
+        interscaleManager_(nullptr),
         lammpsInterface_(LammpsInterface::instance()),
-        list_(NULL),
+        list_(nullptr),
         targetConcentration_(p.value), 
         targetCount_(0), 
         elemset_(p.elemset),
-        p_(NULL),
-        randomNumberGenerator_(NULL), 
+        p_(nullptr),
+        randomNumberGenerator_(nullptr), 
         q0_(0),
         controlType_(p.type), 
         controlIndex_(0),