Simplify personal config as hiera-managed params

This is intended to be exposed and used via hiera. Example usage (yaml):

```yaml
boxen::personal::projects:
  - some_project
  - another_project

boxen::personal::includes:
  - osx::no_network_dsstores
  - osx::global::tap_to_click
  - osx::global::enable_keyboard_control_access
  - osx::global::expand_save_dialog
  - osx::global::expand_print_dialog
  - osx::finder::empty_trash_securely

  - clojure
  - heroku
  - nmap
  - python
  - tmux
  - zsh

boxen::personal::osx_apps:
  - adobe-creative-cloud
  - alfred
  - arq
  - dropbox
  - evernote
  - google-chrome
  - gpgtools
  - hazel
  - istat-menus
  - minecraft
  - omnigraffle
  - playonmac
  - rdio
  - skype
  - slate
  - sonos
  - steam
  - things
  - tiled
  - vlc

boxen::personal::homebrew_packages:
  # Network Tools
  - httpry
  - ipcalc
  - mtr

  # System
  - htop-osx
  - pstree
  - pv
  - spark
  - watch
  - terminal-notifier

  # Dev
  - awscli
  - ctags
  - gist
  - the_silver_searcher
  - jq
  - keybase

  # Mail
  - w3m
  - notmuch
  - urlview
  - contacts
  - msmtp
  - isync

boxen::personal::custom_projects:
  blog:
    source: dgoodlad/d.goodlad.net
    ruby: 1.9.3
  some_other_project
    source: dgoodlad/foo
    ruby: 2.1.2
```