Adding ability to choose initially whether to run with Terminal or iTerm

This can be changed later in Info.plist file at ``/Applications/OpenInTerminal.app/Contents`` by modifying ``OpenInTerminalDefault`` and ``OpenInTerminalDestinationPath``

Fixes: https://github.com/nmadhok/OpenInTerminal/issues/1 & https://github.com/nmadhok/OpenInTerminal/issues/6