OSX: Store Xcode build schemes in the repo

This is necessary to be able to build with xctool, which in turn is
necessary to be able to do CI builds using Travis and Github.
OSX: Add Travis CI configuration

It does "Analyze" on OSX

One outage is that it doesn't fail on Analyze warnings, that needs to be
fixed.
OSX: Fix Travis configuration homebrew invocation

Can't do "brew install xctool" when xctool is already installed, do
"brew upgrade" instead to ensure xctool is at the latest version.
Merge pull request #1 from walles/travis

Add configuration for Travis CI