Feature dictionary scoping lvalue

• Supports using '/' within dictionary scoping, which avoids the ambiguity of having a '.' which could mean scoping, or be part of a keyword.
• General dictionary searcher classes/methods for clearer searching semantics and to enable addressing a dictionary entry as an lvalue.
• The #remove directive now functions across scopes
• Can specify a keyword with a defined scope. If needed, any intermediate dictionaries are created.

For example,

"/boundaryField/lowerWall/type"  noSlip;
"/boundaryField/newBoundary"  { type fixedValue; value uniform (0 0 0); }

Manage "one-shot" change of the inputMode. For example,

#includeIfPresent "user-files"
...
#default value uniform 10;

vs.

#includeIfPresent "user-files"
#inputMode protect
...
value uniform 10;
#inputMode merge    // _Assuming_ we actually had this before

applications/test/dictionary/testDict

@@ -13,18 +13,19 @@ FoamFile
     object      testDict;
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-#inputMode  merge
+
 #includeIfPresent "someUnknownFile"
 #includeIfPresent "$FOAM_CASE/someUnknownFile"
 #includeIfPresent "$FOAM_CASE/someUnknownFile-$FOAM_CASENAME"
 
 internalField   uniform 1;
 
-// use 'protect' to supply defaults
-#inputMode  protect
-internalField   uniform 10;
-dimensions      [ 0 2 -2 0 0 0 0 ];
-#inputMode  merge
+// supply defaults
+#default internalField  uniform 10;
+#default dimensions     [ 1 2 -2 0 0 0 0 ];
+#overwrite dimensions   [ 0 2 -2 0 0 0 0 ];
+// #warn       dimensions      [ 0 2 -2 0 0 0 0 ];
+// #error      dimensions      [ 0 2 -2 0 0 0 0 ];
 
 active
 {
@@ -86,12 +87,12 @@ boundaryField
     #remove inactive
 
     inlet_7  { ${${varType}}}   // Test indirection/recursive expansion
-    #inputMode overwrite
     inlet_8  { $active }
+
+    #overwrite inlet_8  { type none; }
 }
 
-// NB: the inputMode has a global scope
-#inputMode merge
+
 #include "testDict2"
 
 foo