Integration - attribute validation

- Implemented digitsOnly primitive.
- Implemented noSpaces primitive.
- Added unit tests for above.
- Att now manages the lists of valid attributes and modifier names.
- validName migrated to Att.
- validModifiableName migrated to Att.
- New Att::validNameValue.
- Removed obsolete validDescription.
- Removed obsolete validPriority.
- Removed obsolete valid.cpp/guess.
- Implemented text.cpp/noVerticalSpace.
- Added unit tests for text.cpp/noVerticalSpace.
- Removed final static lists from valid.cpp.

src/import.cpp

@@ -175,7 +175,7 @@ static void decorateTask (T& task)
   std::string defaultPriority = context.config.get ("default.priority", "");
   if (task.getAttribute ("priority") == "" &&
       defaultPriority                != "" &&
-      validPriority (defaultPriority))
+      Att::validNameValue ("priority", "", defaultPriority))
     task.setAttribute ("priority", defaultPriority);
 }