[ImgBot] Optimize images

*Total -- 778.71kb -> 683.00kb (12.29%)

/css/images/ui-icons_222222_256x240.png -- 6.76kb -> 4.85kb (28.2%)
/images/mantis_logo.gif -- 7.63kb -> 5.69kb (25.39%)
/css/images/ui-icons_ffffff_256x240.png -- 6.15kb -> 4.81kb (21.88%)
/images/mantis_logo_notext.png -- 10.61kb -> 8.74kb (17.58%)
/doc/modern_view_issue.png -- 164.66kb -> 142.48kb (13.47%)
/doc/modern_my_view.png -- 297.88kb -> 258.47kb (13.23%)
/doc/modern_view_issues.png -- 203.33kb -> 177.60kb (12.66%)
/css/images/ui-bg_gloss-wave_35_f6a828_500x100.png -- 5.68kb -> 5.23kb (7.98%)
/css/images/pattern.jpg -- 6.91kb -> 6.83kb (1.29%)
/docbook/Developers_Guide/en-US/images/mantis_logo.png -- 18.59kb -> 18.37kb (1.2%)
/images/mantis_logo.png -- 18.59kb -> 18.37kb (1.2%)
/docbook/Admin_Guide/en-US/images/mantis_logo.png -- 18.59kb -> 18.37kb (1.2%)
/css/images/ui-icons_ef8c08_256x240.png -- 4.44kb -> 4.40kb (0.86%)
/css/images/ui-icons_228ef1_256x240.png -- 4.44kb -> 4.40kb (0.86%)
/css/images/ui-icons_ffd27a_256x240.png -- 4.44kb -> 4.40kb (0.86%)