Add font colors to config.toml

[hayescode]

trafficstars

Enable option to change primary/secondary font colors for light/dark mode. Useful when using non-standard background colors.

@tpatel @willydouhard Need your guidance here as I'm not a frontend expert and permission issues prevent me from fully testing.

    [UI.theme.light.text]
        #primary = "#212121"
        #secondary = "#616161"
    [UI.theme.dark.text]
        #primary = "#EEEEEE"
        #secondary = "#BDBDBD"

Resolves #673

Example before this PR aims to solve. when setting light mode with the below options: Settings:

[UI.theme.light]
    background = "#17234E"
    paper = "#1F397F"

    [UI.theme.light.primary]
        main = "#f5f5f5"
        dark = "#00CED1"
        light = "#D3D3D3"