ENH: adjustments to Switch

- align Switch more with Enum.
  Now have find(), found() static methods.
  Constructors with failsafe option.

  The find() method makes for clearer coding:

  OLD

     Switch sw(some_string, true); // NB: true = allowBad

     if (sw.valid()) ...

  NOW

     Switch sw = Switch::find(some_string);

     if (sw.good()) ...

  or

     if (Switch::found(some_string)) ...

- improve construct from dictionary to handle all valid token types.
  Previously just read in a word.

- Remove asText() method - replaced by c_str() and str() several
  versions ago.

applications/utilities/surface/surfaceFeatureExtract/surfaceFeatureExtract.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2015-2017 OpenCFD Ltd.
+    Copyright (C) 2015-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -279,16 +279,9 @@ int main(int argc, char *argv[])
                 surfaceIntersection::NONE
             );
 
-        const Switch writeObj = surfaceDict.lookupOrDefault<Switch>
-        (
-            "writeObj",
-            Switch::OFF
-        );
-        const Switch writeVTK = surfaceDict.lookupOrDefault<Switch>
-        (
-            "writeVTK",
-            Switch::OFF
-        );
+        const Switch writeObj("writeObj", surfaceDict, Switch::OFF);
+
+        const Switch writeVTK("writeVTK", surfaceDict, Switch::OFF);
 
         // The "surfaces" entry is normally optional, but make it mandatory
         // if the dictionary name doesn't have an extension