[init] Fix problem with setting the Terminal theme

`Terminal.app` needs to be informed about the theme change, otherwise
it will just overwrite the new settings.
[init] Use xcode-select --install to install XCode

Starting with Mac OS X Mavericks, the `XCode Command Line Tools` can be
easily installed using `xcode-select --install`.

Ref: https://developer.apple.com/library/mac/releasenotes/DeveloperTools/RN-Xcode/#/apple_ref/doc/uid/TP40001051-SW277
[init] Use `homebrew-cask` to install applications

For more in-depth information, please see:

 * https://github.com/phinze/homebrew-cask
 * https://github.com/caskroom/homebrew-versions