Clean source code with a set of code standards

[tdmalone]

Slackemon has been built with only adhering manually to code standards, and also across slightly different environments.

Some older files use tabs for indentations whereas newer ones use spaces. And while the code is generally clean, there's no enforcing of standards and there certainly are parts of the code that should be cleaner.

Need to build an appropriate set of PHPCS rules, clean everything up, and then possibly make it part of the Travis build process.