ENH: simplify objectRegistry access names (issue #322)

New name:  findObject(), cfindObject()
  Old name:  lookupObjectPtr()

      Return a const pointer or nullptr on failure.

  New name:  findObject()
  Old name:  --

      Return a non-const pointer or nullptr on failure.

  New name:  getObjectPtr()
  Old name:  lookupObjectRefPtr()

      Return a non-const pointer or nullptr on failure.
      Can be called on a const object and it will perform a
      const_cast.

- use these updated names and functionality in more places

NB: The older methods names are deprecated, but continue to be defined.

src/functionObjects/utilities/writeDictionary/writeDictionary.C

@@ -160,10 +160,12 @@ bool Foam::functionObjects::writeDictionary::write()
     bool firstDict = true;
     forAll(dictNames_, i)
     {
-        if (obr_.foundObject<dictionary>(dictNames_[i]))
+        const dictionary* dictptr =
+            obr_.findObject<dictionary>(dictNames_[i]);
+
+        if (dictptr)
         {
-            const dictionary& dict =
-                obr_.lookupObject<dictionary>(dictNames_[i]);
+            const dictionary& dict = *dictptr;
 
             if (dict.digest() != digests_[i])
             {