Fix a problem with english-quotes compilation

English quotes weren't initialized. Plus, there's no need for a mixin in defaults.less
If we choose to keep the english-quotes, then it would override the defaults one. Otherwise, we can define our own quotes.
Fix a potential conflict problem in helper.less

Because the mixing get the same name than the following class, some compiler could get confused and crash.
Change the name of the mixing to something different (more explicit).