Add TeamPostgreSQL Cask

This is a weird one. It uses a graphical installer, and a graphical uninstaller which is found in the install directory.

Since there's no support for graphical uninstallers yet, I'm not entirely sure what to use for the `uninstall` stanza.

Also, the graphical uninstaller removes the install directory contents but not the directory itself, which is why I added `"#{Cask.appdir}/teampostgresql"` to the `zap` stanza. This won't work if the user selects a different location in the graphical installer, but I figured it would cover most cases. Is there a better way to handle this?
Well, no. The `uninstall` verb removes the staged path by default; the issue is that the top-level directory created by the graphical installer can be anywhere, but I'm assuming most Cask users would use their usual `appdir`.