Revert "Updated to Unity 4.5."

This reverts commit 18c81becac9e3048f6ff609895374272a9a16a70.
Revert "Updated version."

This reverts commit 578a2179a2c806f807431431113503c800ff49e5.
Fixed a bug where zombie death didn't remove zombie object while sound is muted.
Implemented Android back button on main menu.
Implemented Android back button on results screen.
Increased version.