Replace more strcmp with std::string::compare or std::string::operator==.

This commit also enables TinyXML STL support.
Convert some const char * arguments to const string&
Remove bool CardInstance::hasSubtype(const char * _subtype)

There exists bool CardInstance::hasSubtype(const string& _subtype) and the
const char* version converts _subtype into string deeper in the call
hierarchy anyway. So both methods did the same.
Substitute more char arrays with strings
Speedup MTGAllCards::countByType a bit
Replace even more char* with strings

This might reduce performance a bit since returning strings
by value is more costly than returning const char*. I am not
entirely sure if the added abstraction is worth it.