UI enhancements for plot_trace

- Copy matplotlib styles for figures (look at ArviZ-plots https://github.com/arviz-devs/arviz-plots/blob/main/src/arviz_plots/styles/arviz-clean.mplstyle)
- center axis labels and remove arrow
- normalize to 1 for the KDEs
  - remove y-axis ticks and labels
- Ensure y-axis label is what is selected from the dropdowns