Homebrew bundle

Hey,

in my fork of dev-setup i added the feature to manage brew via [Homebrew Bundle](https://github.com/Homebrew/homebrew-bundle). As it depends on #81 i did not open a PR to avoid showing commits that are not related to the topic.
As soon as a decision is taken in regards of #81 i would like to contribute this change back to your repo if you are interested?

Checkout omares/dev-setup#2 for a clean overview of changes.

> Use [Homebrew Bundle](https://github.com/Homebrew/homebrew-bundle) for brew installations.
>
> Using brewfiles makes it easier for users to customize dev-setup to their needs and it declutters all shell scripts. On top i moved the duplicated brew code into an own script.