Feature: AMOLED Dark theme

[HunterArmstrong]

As a feature for LifeUp I think there should be an AMOLED dark theme (all black) for power saving on newer phones.

[Ayagikei]

Thanks for the advice again.

It's a nice idea.

Currently LifeUp is using AppCompatDelegate to achieve the dark theme. However, it seems that it can not support multiple color set.

Maybe we will replace the current dark theme with a new one that following the Material dark theme guide or figure a way out.

[HunterArmstrong]

Okay. Keep up the good work 👍👍