Update install script

- Remove ksdiff cask as it was removed; The decision was made on the
  phinze/homebrew-cask repository to remove it as they now include it as
  part of the Kaleidoscope cask.  This may present an issue since
  Kaleidoscope is downloaded from the Mac App Store.  Opened a
  conversation with the repository contributors.
- Update install script to make ${HOME}/Applications folder in case it
  isn't present already; all app installation relies on this folder
  being there

Issue: #9