UI bugs and proposed improvements

As time permits, I'd like to post patches here to help improve the UI of OG Management. The layout of the "Manage my groups" page is a little wonky (for instance the horizontal scrollbar with no scroll thumb, placement of the "submit changes" button, etc.) but this fantastic module is just too useful to not use it.

To start it off, here's a simple patch that makes the "Subscriber" text translatable.