Better handle the TK set used for tokens

Let oracle add a basic TK set in cards.xml
Unify all the code previously using the string literal “TK”

cockatrice/src/carddatabase.cpp

@@ -16,6 +16,7 @@
 #include <QImageReader>
 
 const int CardDatabase::versionNeeded = 3;
+const char* CardDatabase::TOKENS_SETNAME = "TK";
 
 static QXmlStreamWriter &operator<<(QXmlStreamWriter &xml, const CardSet *set)
 {
@@ -791,7 +792,7 @@ CardInfo *CardDatabase::getCardFromMap(CardNameMap &cardMap, const QString &card
         return cardMap.value(cardName);
     else if (createIfNotFound) {
         CardInfo *newCard = new CardInfo(this, cardName, true);
-        newCard->addToSet(getSet("TK"));
+        newCard->addToSet(getSet(CardDatabase::TOKENS_SETNAME));
         cardMap.insert(cardName, newCard);
         return newCard;
     } else

cockatrice/src/carddatabase.h

@@ -218,6 +218,8 @@ private:
 
     CardInfo *getCardFromMap(CardNameMap &cardMap, const QString &cardName, bool createIfNotFound);
 public:
+    static const char* TOKENS_SETNAME;
+
     CardDatabase(QObject *parent = 0);
     ~CardDatabase();
     void clear();

cockatrice/src/dlg_edit_tokens.cpp

@@ -146,7 +146,7 @@ void DlgEditTokens::actAddToken()
         return;
     
     CardInfo *card = new CardInfo(cardDatabaseModel->getDatabase(), name, true);
-    card->addToSet(cardDatabaseModel->getDatabase()->getSet("TK"));
+    card->addToSet(cardDatabaseModel->getDatabase()->getSet(CardDatabase::TOKENS_SETNAME));
     card->setCardType("Token");
     cardDatabaseModel->getDatabase()->addCard(card);
 }

oracle/src/oracleimporter.cpp

@@ -235,6 +235,10 @@ int OracleImporter::startImport()
     QListIterator<SetToDownload> it(allSets);
     const SetToDownload * curSet;
 
+    // add an empty set for tokens
+    CardSet *tokenSet = new CardSet(TOKENS_SETNAME, tr("Dummy set containing tokens"), "tokens");
+    sets.insert(TOKENS_SETNAME, tokenSet);
+
     while (it.hasNext())
     {
         curSet = & it.next();