General UI Improvements

[Sma-Das]

1. Add a high contrast mode
2. Dedicated settings button (yes I know cmd + , is a thing but a visual indicator is always nice)
3. Settings font size options -> currently keyboard shortcuts only work for this
4. Custom font support?

[Sma-Das]

+ctrl + tab support to switch between chats

[lukstafi]

High contrast mode pretty please. Related #233 but I want a dark high contrast theme.

[ReidKimball]

I'm on Windows 11. The keybindings to increase and decrease font sizes are inconsident.
To increase it's CTRL SHIFT +
To decrease it's CTRL -

On Windows, increasing font/UI is usually CTRL +, so I'd like it to be that and leave decreasing as it is, CTRL -

[wrick17]

I don't like the monospace font in the user message box. Any option to switch it out for something else would be so great.

[alacritythief]

@Sma-Das @lukstafi I created a high-contrast mode PR: #1284 hopefully it gets reviewed at some point.