ModemManager package should be in repos and installed by default

This request has been made in response to this mailing list conversation: http://trisquel.info/en/forum/no-mobile-broadband-yet-35#comment-4009

There is an issue in Ubuntu Karmic that prevents mobile broadband from working by defaut. This problem affects us in Trisquel 3.5 also.

Installation of the [https://launchpad.net/modemmanager ModemManager] package fixes this issue. This package should be added to our repos and in the default installation so that mobile broadband will work out of the box.