Add Theme Toggle

[jktravis]

The dark theme that was added causes strain on some people just like the light theme for others. Prior work was done to try and use the user's system preferences. But for me, I want my system set to dark, and things that require a fair amount of reading to light for easier reading. Additionally, the current implementation never seemed to respect my settings.

Maybe we should add a theme toggle instead. This theme can be stored in local storage so it will persist.

The toggle here is placed in the top-right corner.

Light and dark look the same on toggle.

[kedashoe]

ty for the PR @jktravis

Only issue I see it the version dropdown is really hard to see

Current version:

With these changes:

[jktravis]

Weird. Mine looks like this in all cases.

I'll see if I can figure out a change.

Thanks.

[yurkimus]

What about system theme?

I never using any toggles related to color scheme and always use "system" approach.

[jktravis]

Can that be overridden? I have two issues that I'd like to solve:

1. it doesn't seem to apply correctly in Firefox (I've tried several different setting permutations between FF and OS).

2. I use dark on my system for most things, but for just text and reading, I find it more difficult with dark mode. For instance, I prefer my mail client to use the darker window borders and such, but he email itself, I need it to be light.

By implementing a toggle of some sort, we can accommodate all personal preferences.

I just didn't know how to implement a toggle while also respecting the color-scheme. If you're familiar with integrating the two, I'd be happy to work with you on it. Feel free to update what I have.