fixed name refactoring
added max_upgrade_counter to limit upgrades
removed todo
refactored, updated and cleaned info bar to display detailed infos about towers and upgrades.
using calculated map_directions to display direction_arrow
cleared info menu after building tower.
added speed up button. close #31. added background image.
moved huds.
enhanced calibration text.
removed debug output.
removed unused function
fixed #56 (closing window with x icon)