Add {OS.newVM ApplicationURL} to create a new VM!

* A std::string is passed so it does not depends of a particular VM.
* The choice of OS is pragmatic, it might as well be {VM.new AppURL}.
* The storage chosen for the appURL is the BoostVM since it needs
  to be accessible from the thread which might start much later.
* The maximal memory of new VMs is hardcoded right now.