Allow empty & Retina fix

[garriguv]

Hey Jan!

Two main changes here:

1. We've been running into issues trying to stamp small icons, we'd like to add an --allow-empty option to just ignore failures if the text doesn't fit.
2. The integration tests were broken on my machine because of Take machine's screen scale factor into account #1. So I fixed that too.

Had to switch BRLOptionParser to use the latest commit because it wouldn't compile on Yosemite.

Hope all is well 😃