Using correct folder names to Rails >5 conventions

[alaxalves]

Fixes #0000 (<=== Add issue number here)

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• PR is descriptively titled 📑 and links the original issue above 🔗
• tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with rake test
• code is in uniquely-named feature branch and has no merge conflicts 📁
• screenshots/GIFs are attached 📎 in case of UI updation
• ask @publiclab/mapknitter-reviewers for help, in a comment below

We're happy to help you get this ready -- don't be afraid to ask for help, and don't be discouraged if your tests fail at first!

If tests do fail, click on the red X to learn why by reading the logs.

Please be sure you've reviewed our contribution guidelines at https://publiclab.org/contributing-to-public-lab-software

Thanks!

[alaxalves]

Changing units/ to models/ and functionals/ to controllers/, deprecating written since Rails >5 has support to such tasks.

[codecov]

Codecov Report

Merging #795 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           development    #795   +/-   ##
===========================================
  Coverage         2.69%   2.69%           
===========================================
  Files               37      37           
  Lines             1742    1742           
===========================================
  Hits                47      47           
  Misses            1695    1695