Use Picasso to load images efficiently

[jmankhan]

I ran into some memory problems and very slow response times trying to load images manually into the menu. I looked into some libraries that could do it better, and I think we should use Picasso (not the same as Picasa). I've added the dependency to gradle and I'll see how the performance is

[jmankhan]

It's working well! I will keep this issue open in case we switch to recyclerview and it messes up a lot of things, which I doubt, but we'll see, eh