Add command to uninstall tunnels

[benwebber]

Continuing #3, we should have a command to uninstall configurations by name:

# Installs configuration as "vpn.example.org"
tunnelblickctl install vpn.example.org.ovpn

# Uninstalls configuration
tunnelblickctl uninstall vpn.example.org

It's not sufficient to remove the configuration from ~/Library/Application Support/Tunnelblick/Configurations or its system equivalent, because Tunnelblick installs backup shadow configurations.

I think we will need to script the Tunnelblick GUI, which may require users to allow tunnelblickctl to control the GUI in System Preferences.