MacOS support

[AndreMiras]

Apparently the app is not building on MacOS:

[23:30] AndreMiras_, btw, I was testing packaging with PyWallet yesterday, it failed with ...zbar....
[23:31] installing zbar on osx was failing...

See IRC logs: https://botbot.me/freenode/kivy-dev/2018-06-18/?msg=101243554&page=2

After fixing it, setup some continuous integration for MacOS to make sure it always build.