Enhanced Dark mode

[langonginc]

1. 建议适配暗色模式下的图标
2. 建议在设置中增加“亮暗转换器” （虽然目前可以通过修改session中的值来实现）

[thekingofcity]

Hi, thanks for the suggestion.

For the second point, RMP will have a dark mode button in the header via #128. You may have a preview at our UAT.

However, the first one needs more tuning as the current icon implementation is a pure JSX.Element instead of a React component. We'll update it later this month.

[thekingofcity]

Hi, the dark mode button is removed. Now RMP will follow your system's default settings and if you want to change the dark mode, use Rail Map Toolkit.

[langonginc]

That's great!