Download and cache FML libs for legacy minecraft versions.

* minor fix for version filtering (1.5 no longer shows forge for 1.5.1 and 1.5.2)
* FML libs are downloaded to mods/minecraftforge/libs and cached
* FML libs are copied to instances which contain FML or forge

logic/LegacyInstance.h

@@ -41,6 +41,7 @@ public:
 	std::shared_ptr<ModList> texturePackList();
 
 	////// Directories //////
+	QString libDir() const;
 	QString savesDir() const;
 	QString texturePacksDir() const;
 	QString jarModsDir() const;