data: Store separate storage version number in SqliteStorage for managing migrations

* deprecated the third version number as storage update number
* version can now have either 3 or 4 numbers
* whether a .coatidb file is outdated is now solely determined by the SqliteStorage::STORAGE_VERSION

src/lib/data/PersistentStorage.h

@@ -49,9 +49,11 @@ public:
 	virtual void finishInjection();
 
 	FilePath getDbFilePath() const;
-	Version getVersion() const;
 
-	void init();
+	bool isEmpty() const;
+	bool isIncompatible() const;
+
+	void setup();
 	void clear();
 	void clearCaches();