Color of squares in History

[HbWang2017]

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In v0.5.3, the date squares are painted depending on how many pomodoros were made in the day. But there is a problem that sometimes the darker square, which means more pomodoros have been made in that day, has less focused time than the lighter square.(Because we may click finish button before the time is out.) Exactly, the square of the day that speending more time focusing on projects is supposed to be painted darker than that have more pomodoros but less time. So, please paint squares in "History" due to the time used that day. thks!!