[ImgBot] Optimize images

*Total -- 172.59kb -> 136.39kb (20.97%)

/Sprites/swoosh.png -- 3.08kb -> 0.52kb (83.1%)
/android/build/res/drawable-nodpi/splash_bg_color.png -- 1.33kb -> 0.30kb (77.13%)
/Sprites/sheet.png -- 10.07kb -> 3.40kb (66.21%)
/Sprites/characters.png -- 12.46kb -> 4.73kb (62.04%)
/addons/github-integration/resources/loading/throbber.png -- 5.47kb -> 3.29kb (39.79%)
/addons/github-integration/resources/github-logo.png -- 2.56kb -> 1.76kb (31.35%)
/addons/github-integration/screenshots/commit.png -- 17.52kb -> 14.96kb (14.63%)
/addons/ch.fischspiele.tilesethelper/AssetLibIcon.png -- 19.51kb -> 16.76kb (14.1%)
/addons/github-integration/screenshots/gist.png -- 30.86kb -> 27.09kb (12.21%)
/addons/github-integration/screenshots/singin.png -- 10.53kb -> 9.49kb (9.93%)
/addons/github-integration/screenshots/repo.png -- 29.91kb -> 27.16kb (9.19%)
/addons/github-integration/screenshots/userpanel.png -- 28.78kb -> 26.44kb (8.14%)
/addons/github-integration/resources/proxy.png -- 0.50kb -> 0.49kb (1.95%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp