Add convenience method Player::get_bonus() #1210

Job	Run time
clickable (Debug, amd64, glew)	11m 16s
clickable (Debug, amd64, sdl)	10m 49s
clickable (Debug, armhf, glew)	10m 50s
clickable (Debug, armhf, sdl)	9m 28s
clickable (Release, amd64, glew)	10m 56s
clickable (Release, amd64, sdl)	10m 0s
clickable (Release, arm64, glew)	10m 25s
clickable (Release, arm64, sdl)	10m 42s
clickable (Release, armhf, glew)	9m 26s
clickable (Release, armhf, sdl)	9m 18s
	1h 43m 10s

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