Automatically configure 3g modules

[johnnyman727]

https://wiki.openwrt.org/doc/recipes/3gdongle gives a pretty good description. It looks like there are two things we'll need. From this repo, we'll need to add a bunch of dependencies. It would be worthwhile to document how big these new deps are. In the CLI, we'll need to add a command for configuring the dongle (which will write to /etc/config/network).