Add more themes

[orhun]

Is your feature request related to a problem? Please describe.

The currently supported themes are listed in README.md and we need more themes!

Describe the solution you'd like

Adding a theme is easy:

1. Add the new variant to BuiltinTheme enum:

flawz/src/theme.rs

Lines 5 to 17 in 32fb9ac

	/// Built-in theme.
	#[derive(Debug, Clone, PartialEq, ValueEnum, Default)]
	pub enum BuiltinTheme {
	/// Dracula.
	#[default]
	Dracula,
	/// Nord.
	Nord,
	/// One Dark.
	OneDark,
	/// Solarized Dark.
	SolarizedDark,
	}

2. Add a new function for the theme colors:

flawz/src/theme.rs

Lines 62 to 89 in 32fb9ac

	/// <https://draculatheme.com/contribute>
	fn dracula_theme() -> Option<Theme> {
	Some(Theme {
	background: Style::default()
	.bg(Color::from_str("#282A36").ok()?)
	.fg(Color::from_str("#F8F8F2").ok()?),
	dim: Style::default()
	.bg(Color::from_str("#282A36").ok()?)
	.fg(Color::from_str("#44475A").ok()?),
	foreground: Style::default().fg(Color::from_str("#F8F8F2").ok()?),
	header: Style::default()
	.bg(Color::from_str("#BD93F9").ok()?)
	.fg(Color::from_str("#282A36").ok()?),
	footer: Style::default()
	.bg(Color::from_str("#282A36").ok()?)
	.fg(Color::from_str("#8BE9FD").ok()?),
	selected: Style::default()
	.bg(Color::from_str("#44475A").ok()?)
	.fg(Color::from_str("#FFB86C").ok()?),
	borders: Style::default().fg(Color::from_str("#44475A").ok()?),
	separator: Style::default().fg(Color::from_str("#6272A4").ok()?),
	highlight: Style::default().fg(Color::from_str("#F1FA8C").ok()?),
	index: Style::default().fg(Color::from_str("#BD93F9").ok()?),
	input: Style::default().fg(Color::from_str("#50FA7B").ok()?),
	input_empty: Style::default().fg(Color::from_str("#FF79C6").ok()?),
	scrollbar: Style::default().fg(Color::from_str("#6272A4").ok()?),
	})
	}

3. Add screenshot in assets/ and update README.md

Describe alternatives you've considered

None.

Additional context

I would love to have a light theme.