[TM-309] Restructure folders

Description

This MR concludes TM-309. Here I make the structure of our folders more consistent (morley package used to reside in the root directory unlike others) and move all code into code/ folder because the root folder grew substantially.

Related issue(s)

https://issues.serokell.io/issue/TM-309

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests (see short guidelines)

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • README
    • Haddock
    • docs/
  • I updated the changelog if my changes are externally visible.

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.