objectRegistry fixes

- objectRegistry gets a rename() that also adjusts the dbDir
- cloud reworked to use static variables subInstance and defaultName.
  This avoids writing "lagrangian" everywhere

string fixes
- avoid masking of std::string::replace in string.H
- avoid old strstream in PV3FoamReader

src/OpenFOAM/primitives/strings/string/string.H

@@ -144,6 +144,9 @@ public:
         template<class String>
         static inline string quotemeta(const string&, const char quote='\\');
 
+        //- Avoid masking the normal std::string replace
+        using std::string::replace;
+
         //- Replace first occurence of sub-string oldStr with newStr
         //  starting at start
         string& replace