A theming protocol for abstracting Luno fonts and colour themes

Theme.swift

protocol Theme {
    static var isLunoV3Enabled: Bool { get }
}

/**
 Theme type dynamically determined based on the `isLunoV3Enabled` flag
 */
extension Theme {
    static var color: ThemeColor.Type {
        isLunoV3Enabled ? LunoThemeColor.self : LegacyThemeColor.self
    }
    
    static var font: ThemeFont.Type {
        isLunoV3Enabled ? LunoThemeFont.self : LegacyThemeFont.self
    }
}