Integrate og features better

@joachim of the British English team pointed out this unfortunate UX issue when he started off on localize.drupal.org. Basically, language teams have two homes. For the British English team:

http://localize.drupal.org/translate/languages/en-gb and
http://localize.drupal.org/languages/en-gb

The first is somewhat connected to the second (there is a group block + a link to the group in the contribution block). The second is however not at all connected to the first. There is no way to navigate back. However, ideally, these two interfaces would be tightly coupled and presented as one. The user should not be bothered with the fact that we have OG and we have l10n_server and these two are different things.

Therefore I decided to abandon this custom and lame attempt to do listing using l10n-server-* taxonomy terms (or better said, relegated that to the non-og setups), and moved in the group front page posts to the overview screen. So now translate/languages/* should display the group front page with our added boxes. I've also added code to have a broadcast tab to replicate this OG feature on this UI.

Since this still means we have two group home pages to go to, I've added l10n_groups init code to redirect to the new version, which is the canonical version now. So if something linked to that, it will redirect to the new group home page now.

This would however fence you off from going to edit the group node or see revisions for it. So I've added a group edit link to the group links list. This is IMHO a good place for this functionality and it looks to work well.

Finally, the "join group" functionality was totally hidden in the group details block. Good luck for people to find it. So I've added a big Join link to the Contribution block with this patch.

I'm going to commit this to the 6.x-2.x branch and deploy on staging and then attach a few screenshots to demonstrate changes. The result is basically that we have a unified UI for groups and translations now.