Remove pause state key binding
Introduce convenience typedef for std::unique_ptr declarations
Introduce winning track on GameOverState and move sounds to GameObject
Change the start new game key binding to Enter (from 'r')
Change selectCard return type to void (from bool)
Bug fix on crash when no cards are selected
Introduce load method for CardView
Move audio listener object to GameObject
Use GameObject's instance of nom::Display
Introduce loading progress feature

  * We probably will not absolutely need this
after music track streaming is implemented...