Clean up static sizing

[h7x4]

There's a lot of places in the codebase where the widgets have either a static width, height, fontsize, padding or margin. Most of these should be sized relative to something else, so that the design doesn't change as much on different screens.

One example is

https://github.com/h7x4ABk3g/Jisho-Study-Tool/blob/17d6f862a280fecc8db71dff5bd7c0d0814fa50f/lib/components/drawing_board/drawing_board.dart#L126-L135