[ImgBot] Optimize images

*Total -- 859.03kb -> 692.46kb (19.39%)

/img/line_title_bg.gif -- 1.07kb -> 0.04kb (96.07%)
/img/testimonials_block_bg.gif -- 1.07kb -> 0.05kb (95.63%)
/img/release_icon.png -- 89.16kb -> 18.35kb (79.42%)
/img/bottom_block_bg.png -- 0.90kb -> 0.29kb (67.9%)
/img/line.png -- 0.94kb -> 0.32kb (66.18%)
/img/grey_quote.png -- 1.06kb -> 0.37kb (64.95%)
/img/fancybox_overlay.png -- 0.90kb -> 0.32kb (64.79%)
/img/tw_arrow_up.png -- 0.96kb -> 0.34kb (64.35%)
/img/over.png -- 0.91kb -> 0.32kb (64.29%)
/img/left_nav_bullets.png -- 0.93kb -> 0.33kb (64.07%)
/img/tw_arrow_down.png -- 0.96kb -> 0.35kb (63.96%)
/img/menu_icons.png -- 0.92kb -> 0.34kb (63.07%)
/img/collapse_btn.png -- 1.69kb -> 0.75kb (55.41%)
/img/slider_arrows.png -- 2.94kb -> 1.35kb (54.08%)
/img/selectnav.png -- 17.03kb -> 8.34kb (51.03%)
/img/paintbrush_w.png -- 1.76kb -> 0.87kb (50.47%)
/img/quotes.png -- 1.80kb -> 0.94kb (47.77%)
/img/follow.png -- 2.17kb -> 1.19kb (45.02%)
/img/socials.png -- 3.68kb -> 2.02kb (44.97%)
/img/date_img_mask.png -- 2.45kb -> 1.35kb (44.82%)
/img/quote.png -- 2.33kb -> 1.30kb (44.26%)
/images/mantis_footer_logo.png -- 13.38kb -> 7.56kb (43.51%)
/img/over_round.png -- 2.92kb -> 1.68kb (42.47%)
/img/figures.png -- 2.88kb -> 1.72kb (40.5%)
/img/socials_icons.png -- 3.12kb -> 2.09kb (33.04%)
/images/mantis_logo_262x90.png -- 40.81kb -> 29.22kb (28.4%)
/images/mt_dashboard_page.png -- 47.81kb -> 36.78kb (23.07%)
/img/warning-icons.png -- 3.42kb -> 2.64kb (22.9%)
/images/mt_login_page.png -- 41.51kb -> 33.40kb (19.53%)
/images/mt_issues_page.png -- 73.24kb -> 59.26kb (19.09%)
/img/button-ie.png -- 14.85kb -> 13.63kb (8.19%)
/img/button-op.png -- 12.79kb -> 11.88kb (7.15%)
/img/button-ff.png -- 16.96kb -> 15.80kb (6.84%)
/img/button-ch.png -- 16.33kb -> 15.31kb (6.23%)
/images/mantisbt_screenshot.png -- 134.98kb -> 126.74kb (6.1%)
/img/note_stick_bg.png -- 55.48kb -> 53.83kb (2.97%)
/twitteroauth-master/images/darker.png -- 2.31kb -> 2.28kb (1.39%)
/img/sticker_small_white.png -- 22.11kb -> 21.86kb (1.14%)
/img/attention_stick_bg.png -- 63.42kb -> 62.77kb (1.02%)
/img/attention_sticker_small.png -- 26.52kb -> 26.37kb (0.56%)
/img/sticker_small_yellow.png -- 26.52kb -> 26.37kb (0.56%)
/img/attention_sticker_sidebar.png -- 51.03kb -> 50.86kb (0.32%)
/img/sticker_sidebar_yellow.png -- 51.02kb -> 50.86kb (0.31%)