foam-extend-3.1 Merge Request #50: Homebrew as a third-party package manager (open)

Corrections to use:
- Homebrew (http://brew.sh) as a package manager for third-party software.
- clang from Apple's CLT for compilation

[Bernhard Gschaider]

I would recommend postponing this merge until we've decided on the strategy for the configuration scripts (merge request #7 is a blocker here). It then should be easier use different ThirdParty-repositories