Added 'native' task

Added a 'native' task in order to run a native console application. I added parameters 'os' and 'targetType' to method 'launchTask', and pass in the previously defined values as parameters from 'iphoneSimTask', 'ipadSimTask' and 'ipaTask'. I also explicitly defined a temporary directory ("target/native"), so that the user can locate the generated binaries.
I haven't tested the i-device specific functionality after the change, but launching a native console application now works on my system.