Ensure that all member attributes are initialized

I ran the game through cppcheck and it spat out a bunch of member
attributes that weren't being initialized. So I initialized them.

In the previous version of this commit, I added constructors to
GraphicsResources, otherlevelclass, labclass, warpclass, and finalclass,
but flibit says this changes the code flow enough that it's risky to
merge before 2.4, so I got rid of those constructors, too.

desktop_version/src/Graphics.cpp

@@ -114,6 +114,8 @@ void Graphics::init()
     tl = point();
     towerbuffer = NULL;
     towerbuffer_lerp = NULL;
+    footerbuffer = NULL;
+    ghostbuffer = NULL;
     trinketr = 0;
     trinketg = 0;
     trinketb = 0;