Update plugin theme VM variables to use _ instead of camelCase

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.2.0 CE M4
• Fix Version/s: 6.1.30 EE GA3, 6.2.0 CE M5
• Component/s: Frontend Infrastructure, Themes Infrastructure
• Labels: None
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-plugins/pull/1397

For our source formatting and consistency of VM files, we need our VM variables to use "_" instead of being camelCased in plugins.

Ex.

#set ($nav_order = "")

instead of

#set ($navOrderClass = "")