Use TTK Styling

- This patch switches from the simple Tkinter widgets to the *themed*
  Tkinter widgets. Different systems (ie. Windows, Linux, MacOS) should
  have a default TTK theme that looks cohesive with the rest of the
  system.
- There are a few other necessary changes. The TTK scales use floats by
  default, rather than the integers used by the TK scales.

Fix black formatting issues