Create StartMenuState class
Made main() start application at StartMenuState. Changed logging to use std::endl;
Add Application::setRunning() method so StartMenuState can signal end
Import MainMenu.png and xcf
Separate menu background from text. Add Logo.png
Add start and quit text for menu
Update logo. Change placement of Quit slightly
Fixed wonky comment
Changed setRunning() to stop()
Fixed stylistic concerns
Renamed logo and menu
Changed comment style
Fixed quit to use correct method
Changed texture loading to use TextureManager. Add to json
Fix call to spritePath()
Changed member names to conform to project style
Delete main_menu_background.png as it identical to chessboard_640x640.png
Got rid of relative path
Fixes CMakeLists.txt library for os x (and possibly linux).

(SFML/BOOST)_ROOT variables were being used regardless of whether or not find_package successfully located a library, which is silly for nix systems. Modified CMakeLists.txt to only use specified "root" variables if and only if find_package doesn't find the library.
Changes requested by LB

Uses directory found by find_package if and only if *_ROOT is not specified.