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/command.cpp

@@ -69,7 +69,7 @@ std::string handleAdd ()
   if (context.task.get ("priority") == "")
   {
     std::string defaultPriority = context.config.get ("default.priority", "");
-    if (validPriority (defaultPriority))
+    if (Att::validNameValue ("priority", "", defaultPriority))
       context.task.set ("priority", defaultPriority);
   }