Implement dark mode on all screens on MainStack

[LucientZ]

Overview

Darkmode is a setting that a user can select which will make the entire app use a dark color palette instead of a light one. This can both save on power and be less straining on a user's eyes. Some people also just find a darker color palette more appealing.

Tasks

• [x] Add darker colors to all screens in and nested in MainStack if darkmode setting is set to true for the user.
• [x] Ensure the colors persist even if the user logs out and logs back in.
• [x] Make sure these changes are saved. This should already be implemented, so only verification is required. (You can do this by making another account, switching to it, and switching back)

Screen Groups

• [x] Settings Screens
• [x] Leaderboard
• [x] User Profiles
• [x] Involvement
• [x] Event Creation
• [x] Event Information

[JasonIsAzn]

I don't know if I mentioned this, but I was also thinking about have some seasonal theme throughout the year. So this would help set that up as well. We haven't gotten approve about seasonal theme yet tho.

[LucientZ]

Seasonal themes shouldn't be too difficult. Usually with those, you don't really change the ui design too much because you want the app to continue working like it did before. We can do things like change trim colors of certain elements, add a pumpkin somewhere in the ui, etc. Things that are non-intrusive.

[JasonIsAzn]

closing issue, this is almost done except for admin screens. The dark mode for admin screens will be done along with #397