Modified PSR2 SwitchDeclarationSniff to support variable $indent

Minor modification to PSR2 SwitchDeclarationSniff to support a variable $indent, rather than using a hardcoded 4 space value. This allows for better extensibility, as without it, there's no way for one to extend the class without having to rewrite the "process" function for variable indent. With these modifications with $indent as a public var, $indent prop can be modified via ruleset rule property override.