bug fix http://bugs.openmw.org/issues/428 - player's death

Appropriate handling of player death: 1)turn POV on or leave POV/preview mode 2)and don't allow to toggle view in InputManager::update (or animation will be played again). 
Main handling is in MWMechanics::CharacterController::kill().
Functions:
Disable return option in main menu func: MWGui::MainMenu -> MWGui::WindowManager
Reenables 'return' at World::startNewGame().
For checking if camera is in first person, getCamera() func: MWRender::RenderingManager->MWWorld::World