Feature - Config validation

- The 'version' command now complains about use of deprecated color names and
  duplicate entries.
- Unit tests verify duplicate detection.
- Unit tests verify deprecated color detection.
- Most validation code moved from command.cpp to Config.cpp.

src/command.cpp

@@ -551,31 +551,8 @@ int handleVersion (std::string &outs)
     out << std::endl;
   }
 
-  // Complain about colors that still use underscores.
-  int countDeprecatedColors = 0;
-  std::vector <std::string> deprecatedColors;
-  foreach (i, all)
-  {
-    if (i->find ("color.") != std::string::npos)
-    {
-      std::string value = context.config.get (*i);
-      if (value.find ("_") != std::string::npos)
-      {
-        ++countDeprecatedColors;
-        deprecatedColors.push_back (*i);
-      }
-    }
-  }
-
-  if (countDeprecatedColors)
-  {
-    out << "Your .taskrc file contains color settings that use deprecated "
-        << "underscores.  Please check:"
-        << std::endl;
-
-    foreach (i, deprecatedColors)
-      out << "  " << *i << "=" << context.config.get (*i) << std::endl;
-  }
+  out << context.config.checkForDeprecatedColor ();
+  out << context.config.checkForDuplicates ();
 
   // Verify installation.  This is mentioned in the documentation as the way to
   // ensure everything is properly installed.