Mass change: new preflight/postflight stanzas

Convert 3 Casks to new DSL forms:
 - `before_install` to `preflight`
 - `after_install` to `postflight`
 - `before_uninstall` to `uninstall_preflight`
 - `after_uninstall` to `uninstall_postflight`

References: caskroom/homebrew-cask#6074, caskroom/homebrew-cask#5890, caskroom/homebrew-cask#4688