Added a black and white menu bar icon and preference to use it, defaulting to current, color icon ala Dropbox.app

Like the title says, I added a black and white menu bar icon and preference to use it, defaulting to current, color icon ala Dropbox.app

It looks like this:

![Screenshot](http://f.cl.ly/items/2W0Z420s2E1m3e05111O/Screen%20Shot%202013-01-04%20at%2012.02.14%20AM.png)

Also cleaned up the .gitignore to ignore CocoaPods stuff, as like rubygems, it's best to keep these files out of source control.