Move submodules to a /modules folder

Problem/Motivation

There is a pattern in contrib to put submodules inside a /modules folder. This makes them easier to manage to developers working on the module, as they are not mixed in with the files and folders of the main module -- e.g. prior to making this change, the listing of the main folder is:

README.md
config
css
img
src
tests
unomi_actions
unomi_conditions
unomi_connect.info.yml
unomi_connect.libraries.yml
unomi_connect.links.menu.yml
unomi_connect.module
unomi_connect.routing.yml
unomi_connect.services.yml
unomi_profiles
unomi_rules
unomi_segments

I've tested and #2651144: Moving modules breaks system is not affecting this.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes