[ImgBot] Optimize images

*Total -- 341.75kb -> 199.00kb (41.77%)

/docs/pcb_back.png -- 81.21kb -> 43.25kb (46.74%)
/docs/pcb_front.png -- 131.72kb -> 74.37kb (43.54%)
/docs/controls.png -- 128.82kb -> 81.38kb (36.82%)

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

Author: ImgBotApp