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/main.h

@@ -37,14 +37,8 @@
 #include "../auto.h"
 
 // valid.cpp
-void guess (const std::string&, const char**, std::string&);
-bool validPriority (const std::string&);
-bool validDescription (const std::string&);
-bool validDuration (std::string&);
 void validReportColumns (const std::vector <std::string>&);
 void validSortColumns (const std::vector <std::string>&, const std::vector <std::string>&);
-bool validAttribute (std::string&, std::string&);
-bool validId (const std::string&);
 bool validTag (const std::string&);
 
 // task.cpp