Remove `AJAX` from the cross-domain section

CORS is not just for AJAX.
Reintroduce MIME type mappings for `ico` & `svg`

Not all Apache `v2.2.x+` servers seem to have the following
`filename expression` to `content type` mappings:

  * `ico` ↔ `image/x-icon`
  * `svg` ↔ `image/svg+xml`

Thanks @matthewlein.

Ref:   h5bp/server-configs-apache#28.
Close: h5bp/server-configs-apache#28.