【feat】frequency/period support reverse mode

[begoat]

For some habits, I want them "at most" frequency/period. We can add one button to mark whether it's a Forward / Reverse habit.

For example, I have a habit called #eat-too-much. I will only track it when i really eat too much. I set the frequency/period to at most 3 days one month. add this feature is useful for me~

[c6p]

Thanks. Wonderful idea. I'll add them in the next version.