Add Depth Parameter to kdb ls

[sanssecours]

Purpose

This pull request contains

• the commits of pull request kdb-ls-depth: Implement depth parameter for kdb ls #1345 (implementation of kdb ls) and
• some other minor changes related to kdb ls.

This pull request closes #1345.

Checklist

• I checked all of my commit messages.
• I ran all tests and everything went fine.

[markus2330]

Thank you both!