BackendUtils: a stricter convertToUrl
BackendUtils: a stricter convertToUrl

work well with strange urls:
  accept "文字.a"; refuse "a.文字" or "http://a.文字/"
fix a bug of adding "http://" header if there's any space

gdh1995/vimium-plus,gdh1995/vimium-plus,gdh1995/vimium-plus