refactor cssplugin for ct to extend
minor refactor to remove knowledge of Virtual plugin which an internal concern and remove a method that doesnt need to be protected
Merge branch 'develop' into refactor-for-cssplugin-extension

Conflicts:
	brjs-core/src/main/java/org/bladerunnerjs/plugin/plugins/bundlers/css/CssContentPlugin.java
Merge pull request #792 from BladeRunnerJS/refactor-for-cssplugin-extension

refactor cssplugin so it can be extended/overridden