Yun, 3G dongle and yun_3g library

[sonnyyu]

@sonnyyu FYI I see you're using the wget trick for packages with "+" in the name: it has been fixed since version 1.2

I knew I am still at version 1.1 , and will update once 1.5.0 is release.
but for my understand the "+" problem is from ISP of "arduino.cc". They should be able to fix it.