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/Context.cpp

@@ -440,7 +440,7 @@ std::cout << "# parse post-termination description '" << *arg << "'"
     }
   }
 
-  if (validDescription (descCandidate))
+  if (noVerticalSpace (descCandidate))
     task.set ("description", descCandidate);
 
   // TODO task.validate ()