Enhance code quality through sonarcloud.io or similar

[ovidiul]

sonarcloud.io is an online service for Code Quality Review, it might be a good idea to set this up along with PHPCS and Wordpress coding standards and it will give way for better code practices and better collaboration.

A current scan revealed a list of potential items that should be fixed.

[GaryJones]

There are a few inspection items that could be addressed, but there are a few false positives in that list as well. Each fixable type should be opened as a new PRs.