PrefixAllGlobals: make independent of case naming conventions

[jrfnl]

I think the PrefixAllGlobals sniff should be more code style independent, i.e. remove the need for an underscore between the prefix and the class/function/variable name.

Should the sniff really care about whether people use Camel_Caps, camelCase, snake_case or any other variant of naming conventions, as long as whatever name is used, is prefixed ?

Just wondering what the opinions are about this.

Related to #763