Use font-family: inherit for elements rather than declaring Avenir Next

[paulcpederson]

Right now we declare:

form, select, button, input {
  font-family: "Avenir Next", "Helvetica Neue", sans-serif;
}

I think we should use:

form, select, button, input {
  font-family: inherit;
}

This seems to work, and will make switching the face for Vietnamese much easier (https://github.com/Esri/calcite-web/blob/master/lib/sass/calcite-web/type/_i18n.scss).