Starting HUD development: HUD main class.

View MantisBT issues #208 and #209
(http://cordobazombie.com.ar/dev/tracker/view.php?id=208)
HUD: creating file structure + classes skeletons
HUD: transitional commit, to keep on in Agus place

Few additions to HUD and HUDelement taken from sample files in:
http://goo.gl/uaYlB7
Useful code exemplifying Ogre::{Overlay,OverlayContainer} usage
comes from ConfigState.{h,cpp} in that link.
HUDelement "weapon" implemented. Testing is due.
HUD: super basic test up and running!
HUD: building properly, but weapon change fails.
HUD: unified HUD update callback.
HUD: added HUDbullet class, with weapon swap logic

TODO: display and update bullet count,
      via Ogre::TextAreaOverlayElement and cz::Weapon*.
HUD: bullet count update on weapon swap.

TODO: HUD firing and reloading update (add MainPlayer callback)
HUD: all functionality finished.

Includes MainPlayer integration via cz::linker::linkMainPlayerWithHUD()
TODO list: add weapon cross in mid-screen?
           fix MainPlayer to fully test integration with HUD.
Merge branch 'HUD' into cordobazombie0.1