Enable / Disable depth writing

[JayFoxRox]

4 commits, 4 comments:

• First this replaces the ObjectData flags for SA with those from GTA3.
  We can still re-add the code later when working on SA. I think this was added for SA by accident anyway?
  This also made it necessary to change some damage handler.
  (No idea what the 80 means btw, I think there should be an enum for these values..)
• Then add a depth write function to the OpenGL Renderer
  (Unused at this point)
• During the previous change I noticed that the blendEnabled bool is never actually set (which always forces enabled GL_BLEND). However, setting it breaks the renderer because the blend state is not recovered on Renderer invalidation and even when adding that it's still broken because not everything invalidates the renderer..
  I didn't want to fix it as part of this commit so I only added a note and made the current operation more obvious (which also should cause a warning during compilation).
• The real change in this one is that objects which have flag value 64 (NO_ZBUFFER_WRITE) don't do depth writes anymore now.
  This avoids the shadow-z-fighting which is commonly seen under the train tracks.
  I've also disabled depth writing for the text renderer but did not test if the actual game does that too.
  I might have a look at text rendering soon anyway and it's easy enough to change it back if it's wrong.