Dutch translation for admin tips plugin

Hi,

I've translated the admin tips plugin into Dutch, so I've attached it for others to use and the awesome devs to include it in the plugin.

https://www.dropbox.com/sh/n1kt22d4fzkf6zh/N7wyK2eI_n/languages

The folder also contains a translation for the Site categories plugin, but that's a WIP.

Davey.