Improve the directory structure

Much of the Kotlin and xml files are relatively unorganized (all residing in one folder). Let's clean this up and organize them (maybe by screen?).
**speak with other devs on the pod before doing this, as this could create some nasty merge conflicts**

Start by inventorying the Kotlin and XML files currently kept in one folder, then speak with the other developers on the pod before proposing an organization by screen. Agree on the target directory structure and coordinate changes to avoid merge conflicts; the work is done when the files are organized consistently under that shared plan.

Written by the indexing model from the issue text.