Use Camel Case for Variable Names

Problem/Motivation

From Drupal's PHP Coding Standards:

Variables should be named using lowercase, and words should be separated either with uppercase characters (example: $lowerCamelCase) or with an underscore (example: $snake_case). Be consistent; do not mix camelCase and snake_case variable naming inside a file.

Proposed resolution

Try to find a tool to automate this, or just do it manually with a smart IDE.

Remaining tasks

Update the variable names.