Fix variable name s/jquery/jqueryCore/g
Throw error when vars.zThemeParams is used to instantiate a new theme
Model's on("change") must be executed before user's on("change"). So, triggering a new event called change:before for that purpose.

- Due to the non deterministic execution order of events, download#themeUrl()
  failed to prevent zThemeParams to be sent together with unzipped params.
  Because, the deferred themeParamsUnzipping had no effect if this.on("change")
  was executed after user's model.on("change"). This issue caused #160, and
  #168. This issue has been fixed by fixing the execution order of the events:
  [change:before, change];
Don't send zThemeParams param when requesting /themeroller/parsetheme.css
Ignore zThemeParams on GET /themeroller
Fixes #171