Rename resonator folder and add missing __init__.py file

[PositroniumJS]

What are the issues this pull addresses (issue numbers / links)?

None

Did you add tests to cover your changes (yes/no)?

No need

Did you update the documentation accordingly (yes/no)?

Yes

Did you read the CONTRIBUTING document (yes/no)?

Yes

Summary

• the folder resonator was not in the installed package because of a missing __init__.py file
• rename this folder resonator resonators for coherence with the other folders of qlibrary
• correct some typos

Details and comments

Renaming the folder is a (small) breaking change

[zlatko-minev]

Have you checked this all runs and works without bugs

[PositroniumJS]

Have you checked this all runs and works without bugs

Now after installation the folder resonators is well installed and showing up in the GUI. If you want to import an element from it you have to change resonator by resonators in the previous imports:
from qiskit_metal.qlibrary.resonators... import ...

The other changes are just typos in comments or documentation, and useless numpy import in two qubits.