Moved brew and cask installs to separate scripts.

Following in the steps of mathiasbynens/dotfiles we separate out application
specific tasks.
bootstrap.sh should be modified to call brew.sh and cask.sh
Removed brew cask installs from brew.sh

These cask installs were moved to cask.sh in previous commit:
SHA: effed653bfb0e134df287bf1922d8a345f2d178e
Changed to executable bash scripts

Updated bootstrap.sh to call bash
Removed comment about Xcode TOS

Xcode is not actually installed.
Things proceed correctly anyways.
Removed MacTex references

We should reintroduce this when it is easy to enable/disable various parts of
the entire setup process.
See issue #2
Added calls to brew.sh and cask.sh from bootstrap.sh