Add MaterialTheme Typography Styling

Instead of manually declaring things like font size and weight, we can use the default MaterialTheme typography settings for sizing headers, content etc. From quickly experimenting, I don't see a need to create custom text sizing, but I believe there are some existing manual font styles we can switch over to the MaterialTheme method.

Here's an example: https://developer.android.com/jetpack/compose/themes/material#text-styles